Understanding and Evaluating Heat Pumps

Heat pumps are a bit of magic. But you use one in your home every day – your refrigerator. So if you can accept that your fridge works, somehow making 0 degree air from the 70 degree air in your home, plus some compressor action, then you should be able to accept that heat pumps can produce 95 degree air to heat your home while it’s 25 degrees outside.

I’m not going to subject you to a full lesson on thermodynamics and the refrigeration cycle. Instead, I just want you to accept the fact that heat pumps work on the same principles as refrigerators and air conditioners – they move energy from one place to another. In the process, they make one side of the system hotter and the other side colder.

Heat pumps, refrigerators and air conditioners all work the same way – they move heat from one place to another, amplifying the effect using a compressor and refrigerants.

Intuitively, you already know some things about these systems. You know that when it gets really hot outside, the air conditioner struggles to keep up. It’s the same as when it’s cold out and the heat pump doesn’t crank out as much heat as it does when it’s mild. Why? Because there’s simply not as much heat available outdoors when it’s 15 degrees as when it’s 45 degrees. So rule 1 of heat pumps is:

  • A heat pump produces less heat the colder it is outside

How much less? If you look at the Wikipedia article on heat pumps, a typical heat pump drops from 100% of its rated output at 47F to 60% at 17F.

The second part of the equation that you already know is:

  • when it’s colder outside it takes more energy to heat your home. (Duh).

We now have two obvious, but vital, pieces of information: 1) a heat pump can’t produce as much heat when it’s cold and 2) your home needs more heat when it’s cold. When you combine these two into a graph, you get the heat pump balance point – the temperature at which a heat pump can exactly satisfy the heating requirements of your home.

Graph of heat pump balance point from Elite Software

The graph to the right was produced by software from Elite Software.

What this means to you

Homes require different amount of energy to keep warm based on many factors: insulation levels, air tightness, home size and indoor and outdoor temperatures among others. These are all wrapped up into a single factor called the “heating load.” This is the blue line on the graph. It goes up as the temperature drops. You have some control over the amount of energy needed to keep your home warm. Adding more insulation and air-sealing reduces the amount of energy needed, so the blue line doesn’t increase as quickly as it gets colder out.

When you do that, you change the equation in your favor. Now the green and blue lines will intersect at lower temperatures meaning the heat pump can keep your house warm when it’s colder out.

  • Weatherizing your home allows a heat pump to keep your home warm at colder temperatures

The green line on the graph is determined by the heat pump. Larger capacity heat pumps put out more heat. That raises the green line which again moves the intersection of the two lines to a lower temperature.

  • Increasing the size of a heat pump allows it to heat your home at colder temperatures

Both of these facts are intuitively obvious. You install a bigger heat pump to provide more heat. You insulate your home so that it uses less heat.

In “real life”, there are practical limits to how well you can insulate and how large a heat pump you can install. At some point, you’re going to be stuck with what you have. In most homes, the balance point (the intersection of the green and blue lines) is somewhere between 35F and 45F. This is why heat pumps have such a bad reputation. What happens when it’s colder than the balance point? The heat pump runs and runs and your house just keeps getting colder!

Backup heat

In order to supply heat when it gets too cold out, heat pump systems almost always have some form of backup heat. In the simplest case, the backup heat is supplied by “electric heat strips.” This is just a giant version of your electric toaster sitting inside the air handler. In other cases, the heat pump will be built into a furnace, often powered by natural gas or propane. The backup heat is controlled by a special two stage thermostat that determines when to run the heat  pump and when to switch on the backup heat.

Why not use the backup heat all the time?

Here’s where things get really interesting. A heat pump is very efficient at producing heat compared with toasters. Higher efficiency means lower utility bills. The measurement of efficiency for heat pumps is called its “COP,” or coefficient of performance. For consumer heat pumps, there’s also a rating called the “HSPF” or heating seasonal performance factor. This number is supposed to give you an idea of the system efficiency over the course of the entire heating season.

The COP is more understandable, so let’s look at that for a second.

Toasters (electric heat strips) are (essentially) 100% efficient at converting electricity into heat. This is a COP of 1.0. Heat pumps typically have COP ratings of 2 to 4, depending upon the outdoor temperature and design of the unit. So the heat pump puts out two to four times as heat for a given amount of electrical energy. Or, put another way, it’s two to four times as efficient so your electric bills are one half to one quarter as much as they would be if you heated with toasters.

Side note: Toasters, portable radiators, space heaters, electric heat strips, baseboard electric heaters, ceramic heaters and even those “Amish electric fireplaces” are identical – they convert electrical energy into heat with a COP of 1.0. Don’t believe the hype. They’re identical. Only the packaging is different. Heat pumps work on different physics so they’re much more efficient.

Now that you understand COP and see that heat pumps are two to four times as efficient as electric backup heat, you can see why you don’t want to run the backup heat all the time! Would you rather have a $100 heating bill or a $300 bill?

How about gas backup heat?

It’s much more difficult to compare the cost of heating with gas vs. heating with a heat pump. Gas and electricity prices are different in every town. And you have to take into account the efficiencies of the gas furnace and the heat pump. There are also safety and environmental considerations. But let’s assume for this discussion that running a gas furnace is more expensive than running the heat pump. Otherwise, there would be no point in using a heat pump, you’d just use gas all the time!

It’s all about the balance point

All of this tells us that you want to run the heat pump down to as low temperatures as possible before you switch over to more expensive backup heat. Unfortunately, this requires diddling with thermostat settings that usually are hidden from consumers or not even available in some thermostats. Why not just use the “default” settings? Because doing so can double or triple your heating bills.

A tale of outrageous heating bills…

I was called in to help diagnose high electric bills in a townhouse. My client paid top dollar for a high-end heat pump and his heating bills went through the roof. For a modest sized home, he was paying $500 a month using a super-efficient heat pump.

It turned out that the installer set the thermostat so that the backup electric heat would come on any time it was below 40F outside. The system went from running at a COP of 3.5 to about 1.5 (the combination of electric backup and heat pump). In our area, it’s below 40F most of the winter, so all winter, the backup heat was running, leading to excessive heating bills.

By tweaking the thermostat, we could reduce the temperature for backup heat from 40F down to 30F or even lower. The heat pump was plenty capable of supplying all the heat that was needed down to about 25F, but to be conservative, we set the switch-over to 30F. This little 10 degree change was enough to reduce the use of backup heat by about half, shaving hundreds of dollars off his winter heating bills.

Reduce the backup heat switch-over temperature to lower your electric bills

Optimizing heat pumps to reduce your electric bills

Let’s put all this together:

  1. More insulation and a tighter home lets a heat pump work at lower temperatures
  2. A larger capacity heat pump lets the heat pump work at lower temperatures
  3. Backup heat costs more to run than a heat pump. Electric backup is two to four times as expensive.
  4. Reducing the temperature at which backup heat comes on can dramatically reduce your electric bills.

Action items:

  1. Add insulation and weatherize your home. This makes it more comfortable and energy efficient year round
  2. When choosing a heat pump for a cold climate, err on the side of a larger heat pump. An undersized heat pump will cost you vastly more to run because it will rely more on expensive backup heat.
  3. Learn when the backup heat comes on so you can see how much it’s running. If it comes on when the heat pump is doing fine by itself, look into changing settings so that the backup doesn’t come on until a lower temperature.

Some more details

Most of you can stop reading and just implement the action items listed above. But you may want to know some of the additional technical details that come into play

Sizing for air conditioning

When you size a gas furnace, you’re not worried about how it affects air conditioning because they’re two separate systems. So almost every furnace has more than ample capacity to heat you home. With a heat pump, the same unit supplies you with cool air during the summer, so when you select a certain sized heat pump, you’re also selecting the size of the air conditioner. This is one of the most important reasons that installers don’t just install the largest heat pump available.

During the summer, especially in humid climates, much of the reason that you use an air conditioner is to remove humidity from the air. The longer the air conditioner runs, the more it dehumidifies the air. If the air conditioner is too large, then it runs for short blasts which cools the air but doesn’t properly dehumidify. This leads to uncomfortable conditions in the house, where the air is cold and clammy. It also leads to wide temperature swings.

In humid climates, get the smallest air conditioner that does the job. This provides the most comfortable, even cooling and best dehumidification.

To make matters worse, in my area of the country (eastern Pennsylvania), we get many days that are mild but humid. This is even tougher for over-sized air conditioners. They might only run for a few minutes an hour to keep the temperature comfortable, but yuck, the humidity is awful! To make matters worse, the high humidity can lead to mold problems.

Catch-22 – air conditioning effectiveness vs. heating efficiency

So, I’ve just told you two contradictory things. First, you want a large capacity heat pump in order to minimize the use of backup heat and greatly reduce your winter heating bills. Second, you want a small capacity air conditioner in order to get the best dehumidification and comfort in the summer. What can you do?

As they say, “it’s complicated.” You have to carefully balance these conflicting needs. And there are things you can do to improve the situation.

  • Make sure you have lots of insulation and your home is properly air sealed.

The better your home is weatherized, the less you need heating and air conditioning. You get fewer drafts and your home is more comfortable. So weatherization is pretty much always the first thing to do. In addition, a tighter home will be less humid in the summer because during the summer the outside air carries the moisture into the house. Reducing outside air infiltration means less humidity and greater comfort. That also makes air conditioning less important.

  • Check your ducts

I’ve written a LOT about leaky ducts so I’m not going to repeat it here. Just know, leaky ducts lead to wasted energy and uncomfortable conditions. That means dry air in the winter and humid air in the summer. And almost all ducts are really leaky (30% on average). Do yourself a favor – make sure your duct system is properly sealed.

  • Listen to your system

You’ve heard of the “horse whisperer” and probably the “dog whisperer.” I try to be the “house whisperer.” You learn a lot by listening to your house, especially your heat pump and air conditioner.

During the summer: make notes about how often the system runs. Keep a notebook with the date, time of day, how sunny it is, the indoor and outdoor temperatures, and the amount of time the system runs vs. the time it is off. Also note how comfortable you feel. This one set of measurements gives you more information about your system than your HVAC contractor can tell you with all their calculations and measurements.

The thing this tells you is how much of your system’s capacity is being used. For example, suppose it’s a sunny afternoon in July. It’s 90 degrees outside and your system runs 20 minutes every hour and is off the other 40 minutes. This says your system is only using one-third of its capacity to cool your home under warm conditions. Unless you live in a really hot climate, where it’s over 100 degrees and humid for long periods, your system is much too large.

On the other hand, if it’s 85 degrees and humid and your system is running constantly and you’re still not comfortable, then you’ve got a problem. Either you’ve got really bad duct leaks, your home is poorly insulated and air sealed, or your system is not working properly. Regardless, you’re probably wasting a lot of money. Time to get it serviced.

During the winter: Keep the same notebook and also log when your backup heat is coming on. You can usually tell this because most thermostats have a blue light that comes on to tell you that the backup heat is on.

Your best bet is to monitor the system at a few temperatures. Try 45 degrees, 40 degrees and 35 degrees. If your system is properly sized and configured, your backup heat should almost never come on at these temperatures and you should be able to get a good idea of the system’s capacity.

For example, suppose the system runs for 20 minutes per hour at 45 degrees, 30 minutes per hour at 40 degrees and the backup heat comes on at 35 degrees so the system only runs 15 minutes per hour (because it’s now heating with heat pump plus backup heat).

This tells me that the backup heat is coming on too soon. If the heat pump is only operating 30 minutes per hour at 40 degrees, it could probably handle having the backup heat not come on until below 30 degrees. On the other hand, if the heat pump struggles to keep up at 40 degrees (maybe running 50 minutes per hour) then it’s likely undersized or there’s other problems (just like when it couldn’t keep up with a modest air conditioning requirmement).

Putting the information together:

So you’ve got your notebook and you know that your system is properly functioning. The ducts aren’t leaky and you’ve got plenty of insulation. Now you want to upgrade your heat pump/air conditioning unit. How do you put it all together?

  • Compare the heating and cooling notes under typical summer/winter conditions

For example, where I live, I’d look at how the air conditioner runs when it’s 85-90 degrees and the heat pump when it’s 25-30 degrees. This covers about 90 percent of the conditions the system needs to run.

How much does the system run under those conditions? Does the air conditioner run much more or less than the heat pump? Does the heat pump need lots of backup heat to keep up with the heating demands? Or are things well balanced?

Typically, if you’re in a “heating dominated climate”, you’ll find that your air conditioner won’t run much and the heat pump will run too much. If you’re in a balanced climate, then the system will likewise run about the same in winter and summer. In my climate, I like heat pumps to be able to keep up down to 25-30 degrees, otherwise the backup heat runs too much. The problem is, this will lead to air conditioning that runs too little. What to do?

Two-stage heat pumps to the rescue

Higher end heat pumps (and many mini-split heat pumps) have compressors that can run at different speeds. This allows the system to vary its capacity as needed, giving more efficiency and comfort during mild temperatures and the capacity needed for extreme temperatures. Or, if you live in a climate like mine, it allows the air conditioning to run on low capacity and the heating to run on high capacity, providing the best of both worlds.

This is why I always recommend that people install multi-stage heat pumps. Over the course of the year, they’ll save hundreds of dollars and they’ll make your home much more comfortable year round. So even though it might cost a couple thousand dollars more to install, it’s well worth it.

The key thing with a two stage heat pump is to size it large enough to satisfy most of your heating needs if you live in a heating dominated climate. If you size it too small, then you may as well have saved your money and bought a single stage system. But how to decide how large?

Remember the notebooks? Refer back to them. How big is your current system? Was it big enough to handle your winter heating needs without turning on the backup heat? If so, you should probably keep the same sized system. But if it couldn’t keep up with the heating needs at 40 degrees, then you probably need a system at least one size larger. Just don’t go crazy or the system may still be oversized for air conditioning even at the low setting. It’s all a balance.

Install a two-stage or variable speed heat pump if at all possible. It will make your home more comfortable and energy efficient year round.

Other references

Carrier variable speed heat pump – Infinity heat pump with Greenspeed intelligence

Department of energy – Energy savers: Air source heat pumps

Energy Star – Air source heat pumps and air conditioners


94 thoughts on “Understanding and Evaluating Heat Pumps

  1. Thanks for you thoughts from my earlier post Aug 17, 2018. I just got another estimate from a small local company, father and son that sell Comfortmaker, owned by Carrier. His estimate was for a 3 ton variable speed heat pump (CVH8) and a 4 ton variable speed air handler (FCM4X), Aprilaire filtration Merv 11, new line set, new thermostat, 20kw heat strip. 17.5 SEER 9.0-9.5 HSPF. $8,570.00. Do you know anything about Comfortmaker (other than owned by Carrier)? 4 ton air handler too big? 20kw strip too big? 1572 sq ft brick ranch, triple pane windows, attic insulated properly. Wife is cold in the winter with 28 yr old 2 ton Bryant pump and 2.5 ton Trane Air handler, 15 kw strip.
    Thanks Ted.

    • I’ll start by saying that I am not familiar with that brand. They do appear to have good warranties on the higher end models. I’m not sure why he’s quoting a 4-ton air handler, but if it’s variable speed, he might be able to configure it to reduce the max output so that it doesn’t overpower your duct system. It may be that he’s just trying to unload old inventory, which isn’t necessarily a bad thing if it’s heavily discounted.
      20kW is a lot of heat strip – that’s more than a 5-ton heating system. The problem with over-sized heat strips is that it consumes a huge amount of energy when in operation and could lead to short cycling meaning more discomfort. I would disconnect half the strips and just run it as a 10kW heat strip. This would allow it to be used in conjunction with the heat pump at lower temperatures without totally sucking down power.
      The thing that bothers me about the entire deal is that it’s somewhat indicative of an installer who doesn’t really know what they’re doing. Since the quality of the installation is critical to how well it will work (and hence your wife’s comfort), I’d be very hesitant to trust them. Even discounted, that’s a lot of money and could lead to a lot of frustration in the future.
      That said, the higher priced systems don’t guarantee that the installers are qualified. You’d really have to do your research into the installers. Go with one who knows what they’re talking about and whom you trust.

      • Thanks Ted. One additional comment regarding the higher end system from Carrier that I discussed previously. The 15kw heat strip has the ability to come on in 5kw steps as needed and has the capacity to extract heat from a lower outside temp before the heat strips are needed. Also, I am hoping that the money I save monthly on my electric bill (currently $175 monthly level billing, total $2100 yearly) I can put towards the total cost of the multi stage system. Projected savings of 47% yearly on my electric bill to approx $82 month-$987 yearly. I figure if i am going to do it, I am going to do it once. I really don’t want any regrets with my wife being cold in the winter. I guess we will see.

        Thanks again for you help. I really do appreciate it.

      • Sounds like a good plan. I’m glad the higher end system has staged heat strips – that’s definitely going to help the system work much more efficiently overall.

  2. Pingback: Home Repair: What’s The Best Way To Select Windows For Heating Efficiency? I Have An Older House In A Northern Climate. ~ diy-home-repair.vwx.info

  3. Great post Ted, I had a problem with high heating bills when my heat strips came on, then I had a smart heat strips kit installed and my power bill dropped a lot. I had my HVAC dealer buy the kit at http://www.smartheatstrips.com, they said it makes the heating element modulating instead of just on or off, now it just uses only what is needed in my house.

  4. Ted, great summary!

    I have a somewhat leaky 2-story vacation home at the coast on the eastern shore of Virginia. I’ only visit eight or so times a year, in all seasons, for several days at a time, but it’s important to me to be comfortable when I’m there. I have a heat pump upstairs (size unknown) and an oil furnace and central air conditioning downstairs. (The downstairs is about about 25 percent larger than the upstairs). The The oil furnace is expensive to run and breaks down a lot, so I’m planning to replace the furnace and the air conditioner (which works fine) with a heat pump.

    My contractor recommended a 2.5 ton HP, but said I could probably go with a 2 ton, although the larger would be able to heat and cool better and would make a noticeable difference.

    When I’m not there, I set the thermostat at 55 in the winter and around 82 in the summer. When I’m there, I like it around 75 in the winter and 72 in the summer. I’m 73 and have always had a rather narrow comfort range.

    I’m leaning toward the 2-ton, if it can maintain those temperatures when I’m there. I also like the idea of it running more constantly, as I think that might cut down on drafts in the winter and humidity in the summer.


    • Hi Dottie,

      The simple answer is that it’s impossible for me to make a recommendation without a detailed analysis of your home or it’s previous energy usage. In light of this, it would be irresponsible for me to recommend 2.5 ton vs. 2 ton.

      You note that you oil heater is expensive to run. The question I’d ask is “why?” Ignoring the reliability issues you are having, if the furnace costs a lot to run, that typically means that your house is placing a large demand on it. This would be true of a heat pump also. So the first thing to do is have your home analyzed for overall insulation and energy efficiency. You’ll find that a tighter, better insulated home will be more comfortable regardless of the type of heating system you have. Only after doing this would I consider changing the heating system.

      So my main recommendation would be to have an independent energy auditor work with you to review your home and specific needs. I say “independent” because too many auditors are associated with HVAC or insulation companies and you want someone who doesn’t make money based on other things you buy. A good auditor will be able to analyze your existing fuel usage and tell you if that’s in-line with what it should be for a home in your area. They should also be able to run calculations to approximately determine what your heating costs would be with a replacement system and would be able to walk you through the pros and cons of other systems. For a few hundred dollar investment, the auditor should be able to guide you through the process and tell you what home improvements will make the biggest impact so you can put your money into the improvements that are the most important. In the long run, this will help you live in the most comfortable, efficient and safe home.

  5. Ted-

    First time home owner and we are building. The home will be in a colder region of the mid-Atlantic. Because we are tearing down (the home currently has oil) and building from scratch I do not have the luxury of having any background in this area – I have read a lot but I was wondering if you could give me some clarity as to why I have gotten so many different bids. I am looking at a geothermal heat pump. These are my options for a 2,900 Sqft house – the living room/kitchen is open concept. And we will have a tight house isolation wise when we are done.

    option 1: a first floor and a second floor 2 ton, two stage heat pump each with 60,000 BTU and 97% efficiency (propane backup) – Climate Master Tranquility 30

    option 2: a single 4 ton heat pump with two zones (don’t know specs)

    option 3: two – 2 stage hydron module heat pump (split halfway down the center of the home)

    option 4: a single 5 ton heat pump (with electric backup) – Climate Master Tranquility 30

    I know there really is not enough information with each of these, but my main question was how I could get bids for a single pump both 4 and 5 ton and then also get bids for two pumps. Obviously, the two pumps are going to cost more than the one but will a house of this size with good insulation be able to utilize only one? I read that many companies are over-sizing so I was curious your thoughts on the need for the additional pump. Option 4 is by far the cheapest option and 1 and 2 very similar in price, while option 3 is the most costly.

    I have also gotten a variety of bids on propane as well and thinking out of the box was also considering using my existing oil furnace (in good condition) as a backup or to run our in-law suite separately if that will allow me to utilize a cheaper single heat pump option for the rest of the house. It seems that my home size is right on the tipping point and I would love your thoughts and suggestions.

    Thank you for your time,

    • As you alluded to, this can get pretty involved with many details that factor into the optimal solution for you. I’ll do my best to answer with generalities that, hopefully, you can apply to your particular house.
      Generally, you’ll find that having multiple, smaller systems allows you to make your home more comfortable at a lower operational cost. Since you mention an in-law suite, I should note that having a dedicated unit or zone for that area should be considered almost mandatory. The heating/cooling requirements for the elderly are often vastly different than for younger people. Without multiple units or really good zoning, you will likely encounter serious “thermostat wars”. So based on this factor alone, I would spend the extra money for some form of multiple zone control.

      Back to your question regarding widely ranging prices. HVAC contractors’ prices vary widely even for seemingly identical systems. Unfortunately, buying an HVAC system is vastly more complicated than buying, for example, a car. Therefore, the single most important factor in your ultimate satisfaction with your system is going to be the quality/experience of the installer. With geothermal this is even more true because of the significantly greater complexity of those installations. So I would highly recommend learning as much about geothermal as you can so that you can ask the prospective installers intelligent questions to determine if they know what they’re doing. This is actually what led me to getting into the energy business in the first place! As an engineer, I spent time learning about ground loops, ground thermal conductivity, loop grouting, Manual-J sizing calculations, seasonal ground temperature variations, etc. etc. It was extremely discouraging to learn that the majority of the so-called geothermal experts knew little more about the science of geothermal than was on the spec sheet.

      It can be a daunting task if you’re not highly technical. But there are other things you can do to assess the quality of a potential installer. Here’s a few questions to ask:

      • How long have they been installing geothermal systems?
      • How many geothermal installations have they done?
      • What geothermal specific training have they taken and what certifications do they have?
      • How will they determine the proper size for the system?
      • What type of ground loop will they install?
      • How big a loop will they install. If vertical loop, how deep will the well or wells be?
      • Can they explain the relative benefits of horizontal vs. vertical loops and how they apply in your climate?
      • Will they take you to a couple of their installations so you can see the quality of their work? (if they do good work, they’ll be proud to show you. If they’re shady, they’ll make excuses about customer privacy or come up with other reasons why you can’t see their work)

      These should be easy questions for a competent HVAC company familiar with geothermal.
      A big red flag will be if they don’t ask for your home’s architectural drawings and specifications for windows, insulation, etc. It is impossible to properly size an HVAC system without this information. And since a geothermal installation cost is highly dependant upon the size of the system, it’s very important that it be properly sized. For example, 5-tons of capacity requires approximately 800′-1000′ of vertical loop. At $20/foot, that alone is $16,000-$20,000. A 4-ton system would require proportionately less loop depth so the cost might be $13,000-$16,000. This can then factor in to your insulation and building material choices. I.e. going with spray foam instead of fiberglass can easily result in a house that is that much more efficient.

      That should give you some things to chew on. If you have more questions after talking with the contractors, feel free to ask.

      By the way, one great way to find knowledgeable contractors is to talk to a good energy auditor in your area. An experienced energy professional will know which companies do good work and which to avoid. You might even see if you can hire one to handhold you through the process. It’s complex enough and a large enough investment in your future that it’s worth paying for professional assistance.

  6. Ted, i live in west central Ohio, near Columbus. I am looking to replace my 20 year old air source heat pump. I of course have no idea what SEER or HSPF the old system is but I am looking at Trane XR 15 single stage or XR 17 two stage both 2.5 ton. I have insulated my attic and have replaced all my windows with triple pane vinyl replacements but my walls our prob not insulated the best- 1500 sq ft brick ranch built in 1978. The estimate for the XR 15 matched system was approx $4,600.00. I do not have an estimate for the XR 17 matched system. I guess I would just like your thoughts on my situation. Currently my elec bill is $206.00 even billing-all electric house. I did use my elec backup a few times last year-ouch. Please let me know any thoughts. Just trying to do my due diligence. Thanks.

    • Patrick,
      Sounds like you’ve got a decently efficient home with low electric rates.
      Your HVAC contractor should be able to tell you about your existing system. Most have the technical data available on line in some form. But probably, with that age, you’re probably lucky to have something around 10-12 SEER so either of the systems you’re looking at now would should reduce your electric bills as long as they’re installed well.
      Deciding between a single stage and a two stage may be a simple matter when you get the second quote – often the upgrade price is prohibitive. But if it’s not too bad, say $500-$1000 more, then it’s worth considering.

      How well did your old system perform? Did it keep your home comfortable and control the humidity in the summer? If it did, then there’s probably little reason to go for the two stage. But if you felt like it wasn’t controlling the humidity well, then the two stage would help the situation by running at a lower output for longer, which helps reduce humidity better. It also gives you a more even heat when the temperature isn’t too cold – say 45-65.

      Hope that helps.

      • Hello Ted. I has been a while since we last discussed(2015) my heat pump situation here in west central Ohio. The time has now come to replace the 28 yr old single stage system. Refrigerant leak and R22 being phased out. I won’t bore you with all my estimates just 2 from the same company and both Carrier systems. 3 ton Heat pump, 3 ton air handler, air filtration-Merv 8 or 11, replace the line set (2 companies were going to flush the line set.). Thermostat, 15kw heat strip.
        #1. Carrier Performance 25HCB636A003 2 stage heat pump, Carrier FV4CNF003L00 variable speed fan coil air handler. AHRI reference #9156148. SEER 16.0 HSPF 9.0
        $10,872.82. 0% interest 48 mos.= $226.52 month

        #2. Carrier Infinity variable stage (5 stages) 40%-100% 3 ton heat pump, Carrier 3 ton FE4ANF003L00 variable speed fan coil, same but “FREE with coupon” filtration system, same 15kw strip. AHRI #9893049. SEER 16.5 HSPF 9.5 $13,209.39
        0% 72 mos= $183.46.
        What are your thoughts Ted. Thank you very much.
        Springfield, Ohio 45502
        ps- I was told by 2 companies that R22 and R410 oils don’t mix together and can cause copper to corrode. Replacing the line set is advised by these companies.

      • Given the age of the lineset and the expense of getting a new system combined with the much higher pressures used for newer refrigerant, I’d personally want fresh lines.
        Regarding choosing between the two models, a good 2-stage for several thousand less sounds like a pretty good deal. It would be hard for me to justify the added expense of the Infinity system.

    • Ted, thanks for your thoughts. The system does well in the summer with the humidity and i tend to set the temp to between 65-68 because I like it colder. Like I mentioned, the humidity if fine. So maybe the single stage is ok but depending on the price, correct?


      • Hi Ted, A correction to my previous statement. My current system is a 2.0 ton not 2.5 as I stated earlier. 20+ year old Bryant. The original old thermostat allows me to switch on the backup when I feel I need it and I used the backup several times last winter but I do not know the kilowatts. The 2 ton does well with the humidity (west central ohio). I keep the thermostat at about 68 in summer and maybe 70 in the winter.

        So my question is- Is going from an old 2 ton to a new 2.5 ton too big? Still considering Trane XR 15 or XR 17.

        Thanks for your help,

      • If you do upsize then the XR17 would be a better choice since the two-stage operation would allow it to continue providing appropriate summer performance. With the single stage, you’d get less effective dehumidification and more chance of short-cycling. The higher capacity of the 2.5 ton would help provide more efficient cold weather heating as long as the backup strips can be locked out until needed. Some systems are pre-set to turn on the backup at 35F, which somewhat defeats the greater output of the larger capacity heat pump, so that’s something to check out with the company you’re working with. I like having heat pump thermostats where the switchover temperature is controllable so that I can turn down the switchover temperature and squeeze every bit of capacity out of the heat pump for the greatest efficiency.

      • Hi ted, Do you know which companies tend to make the “best” air source heat pumps. I realize that the installation is just as important. As I mentioned earlier, I am looking at Trane but I am not committed to any brand as of yet.


      • Hi Ted. I appreeciate all the advice. One last question, how are/is the backup electric heat strips sized/matched for an air source heat pump. I believe they are measured in kw but how is the size chosen to match the heat pump?

        Also, still considering Trane and Carrier- as of today can’t get on Trane’s website. Don’t know why but 0% financing is offered intermittently. Carrier’s Wells Fargo credit card is 27-28% charge. Carrier not offering rebates on air source heat pumps just geothermal. The financing difference alone would make me choose Trane.

        Thanks again for the info,
        Patrick Kuss
        Springfield, Ohio.

      • Patrick – each kW of heat strip puts out about 3400BTUs/hr, so about 3.5kW = 1 ton. From what I’ve seen, installers often put in 15-20kW, regardless of heat pump size. I think the logic is that the heat strips will be used when it’s too cold for the heat pump to satisfy the heating requirements and in emergency situations, so better to have too much capacity than too little.

        That said, I’ve worked with a couple people to add manual overrides to reduce or disable the heat strips. For example, under normal conditions with a properly sized heat pump, you might only need 5kW except in extreme conditions. Doing this has substantially reduced these people’s electric bills since the heat strips often come on when there’s still plenty of heat pump capacity (i.e. 35F). I wouldn’t recommend this for everybody, but if someone is looking to really get the most out of their system, this is a good way to go. Best would be to have a multi-stage thermostat and a set of heavy duty contactors (big relays) that could properly stage the heat strips. I.e. 5kW / 10kW etc. Properly designed systems do exactly this but few installers actually do it.

        On the costs, if the installer is good and the price is right, then Trane would likely serve your needs well for many years.

      • Hi Ted.I have been keeping notes as you suggested on my 20 year old, 2.0 Ton Bryant, air source heat pump. Late June, the outside temp has been 90+ with high humidity. Thermostat (old thermostat) set at 69. The heat pump is on for 18 minutes and then off for 12 minutes. Plus or minus a minute or so. Total of 36 minutes per hour on and 24 minutes off. Temp and humidity in the house is fine. Do these numbers have any significance? Thanks.

      • Sounds like the system is working well and even with the old, small 2 ton unit, it’s keeping up nicely with the cooling demands this summer. Given that, I wouldn’t mess with it too much when you upgrade.
        Since you’re using a heat pump, there could be a benefit in going with a 3-ton, two stage. It would probably run in first stage all summer. The benefit would be more heating capacity in the winter. But in all likelihood, the large added expense for two vs. one stage probably wouldn’t be worth it. If you could get a really good deal on it, it might be worth it.
        The other thing to consider is repair costs. I was just talking with an HVAC guy who was on his way to replace a two stage compressor and he said that when they go, they’re super expensive whereas the single stage units are commonplace, so relatively inexpensive. One repair like that would wipe out a lifetime of efficiency gains.

  7. Ted I could use your help. A few months ago I replace my 20 yr old electric furnace with a 4 ton Carrier Greenspeed Heat Pump with Fan Coil and 20kw heat strip, plus Carrier Wifi Thermstat and also had a whole house bypass humidifier (Generalaire 1099) installed. Generalaire 1099 is specified for up to 3000 sq feet and up to 19.2 US gallons.

    Since that time, we have been experiencing very dry air in the house. Our house is approx 2800 sq feet and has moderate tightness. The bypass humidifier is controlled by the Carrier WiFi Thermostat and the continuous fan is selected to auto and the required humidity is set to 40 to humidify with continuous fan on.

    Our humidity levels are about 27 to 30% and the humidifier is running 24/7. Contractor can’t find anything wrong with the humidifier nor with the settings on the thermostat. I’ve noticed that on the Carrier Wifi Thermostat, under the energy usage button, the display indicates that hardly any kw is being used for the continuous fan (1 to 2 kw per day) and I would have expected more like 10 to 15 kw per days usage.

    Wondering if the really low humidity is a limitation of the greenspeed heat pump system functionality or if there is a problem. My contractor has been out twice to look at it and has replaced the original bypass humidifier which was only 17 US gallons with the larger 1099 model (19.2) US gallons but absolutely no difference in humidity levels.

    Any ideas?

    • Derek,
      Dry air is often a hint that there are leaks in the air return part of the duct system. When the ducts are in the attic or other space outside the tight living environment, cold, dry winter air gets sucked in and helps to dry out the air in your home.
      You can get the same effect with air leaks on the supply side because the lost air has to get replaced and the only place it can come from is the outside.
      I’ll have to check out your model humidifier to see the expected energy consumption. For reference however, consider that a good tight house shouldn’t require a humidifier. After I tightened my house and HVAC systems, all our dry air problems vanished. Even with the record cold this winter, I never felt like we needed more humidity.

    • Just checked the manual – which version of the humidifier do you have? There appear to be three. There’s the “power” model, the “drain” model, and a “recirculating” model. The manual also has a troubleshooting guide which might help.

      None of them should use much electricity since they’re mostly passive, using evaporation from the passing air flow to humidify. In theory, this would be very efficient. However, one thing to consider is that a heat pump puts out air at a much lower temperature than a furnace. That also means a much slower evaporation rate, so that humidifier rating would be substantially reduced when used with a heat pump. This is reinforced by their website that says: “19 GPD (Based on 120° Plenum Temperature).”

      This doesn’t answer your question about energy use with the fan running 24/7. As you noted, you’d expect much more than 1-2kWh/day. Perhaps when the fan is on for the humidifier, it runs at a much lower level? Can you tell by the sound of it whether it’s running normally or slowly?

      I also came across this chart in their specifications.

      Also note in that same chart they mention using 140F hot water in the humidifier for heat pump applications. I will caution you however that I have had clients that experienced high utility bills when using hot water for humidification.

      • Ted I just checked, I have the 1099 LHS humidifier model. Interesting about what you mention about the air return, wasn’t aware of that and will look into it. Great tip.

        I have the heat strips locked out on the heat pump on the Carrier thermostat until 5F which is the lowest setting the system allows. When the temps have been high enough over the past few months, to permit the heat pump to supply all of the heat without the heat strips, humidity levels are in the upper 20’s to approximately 33%.

        We’ve had an extremely cold winter so, the heat strips have been running regularly and then the humidity really drops to mid 20’s%. This has caused alot of my wood trimwork (moldings, baseboards etc…) to dry out so much so that the caulking has all cracked and I’ll also have some repairs to do to the hardwood floors as well.

        I’ve also observed that the warm air from the heatpump isn’t nearly as hot/dry as the air that is produced when the heatstrips are activated. Many times this winter the temps have dropped to below -20F (pretty well every day in February) and I’ve found that the heat pump is pretty well non-productive at those temps even though I haven’t locked it out at any temperature, so it got really dry around the house.

        I noticed as well that the energy indicator button on the Carrier thermostat for the continuous fan would sometimes have a larger draw (10 to 15 kw) but for the past month or more its generally only been 1 to 2 kw per day. I wonder if the comment with reference to the fan running at slower speeds than it should be is the cause of that and will check that out with the contractor.

      • I think the energy tracking numbers for continuous fan is a red-herring. I believe that is reporting the energy used to run the fan when it’s not otherwise needed for heating. In these colder months, the heatpump (or staged power strips) try to run continuously and temperature is controlled by varying heat-pump output and/or heat strip stage (I think 20Kw is 5-15-20). So the fan is probably running all the time, but only recording ventilation energy when the air-handler is doing only that.

        Try a console humidifier. If that works, I’d suggest you look into Carrier’s steam humidifier. It has greater capacity and should work better in the heat-pump system. I don’t know why your contractor hasn’t mentioned it. They are rated at up to 34 gallons per day, but be careful what you wish for, if you really are getting 20 below zero temps, I’d try to keep the humidity as low as possible while still maintaining comfort and preserving your furniture. Driving your home to 40% or 45% could cause condensation and mold problems.

      • That additional info about your climate is very helpful. At those low temperatures, the humidity in the air is virtually non-existent, so I’m not surprised that you might need some humidification. Not to say that there still may be issues with the ductwork or air distribution system but it means that even small leaks could significantly dry out your air.

        Let’s put this in perspective with a back-of-the-envelope calculation. Suppose your air handler moves 2000 CFM (cubic feet/minute). A 3000 SF home has a volume of about 30,000 CF, so under ideal conditions, every 15 minutes the air handler turns over all the air in your house.

        Now, suppose you have a 5% duct leak to the outside (5% is low by national averages). That means, every hour it runs, the air handler introduces 6,000CF of outside air at ~0% humidity. When mixed with the 30,000CF of (for example) 40% humidity air in the house, you’ll lose 20% of the moisture, reducing the humidity to 32%. With the blower running 24/7, assuming no additional humidity is added, you’ll quickly approach 0% humidity in the house. It’s vicious.

        All that said, even with a relatively good duct system, you’ll be fighting serious humidity loss as long as the system runs when it’s that cold out.
        Check to see whether the humidifier is using hot water or cold water. It might also mean that you need more active humidification (as opposed to an evaporative system) since you’re using a heat pump.

        Finally, I have to warn you that the combination of dumping lots of moisture into a house and very cold temperatures can lead to serious moisture/rot issues if that humid air gets into enclosed roof cavities. This often happens when there are recessed lights in cathedral ceilings. I bring this up because there can be lots of unintended consequences. In my climate, we strongly recommend that people not add moisture because of these complications. In your climate, builders have to be even more careful.

      • Ted, really appreciate your having taken the time to respond. You have a great website and it was one of the places I looked at in detail prior to making a decision to get a heat pump installed. Lots of great advice in your response and now I finally feel I have somewhere I can go with this.

        Thanks again

    • Ted is right about a tight house needing little or no supplemental humidity. I don’t know what your location is, but a 30Kw electric furnace is about 100MBtu/hr, which is a big furnace for a 2800 sq ft house, so I am assuming it is a cold climate and that the house is not air sealed or well insulated. Knowing the location and the approximate electrical usage in previous years with the furnace would help to understand the demand.

      All that said, Ted points out that leaky ducts can cause your humidity problems. I agree. The heat pump system operates at a significantly lower output temperature than an electric furnace. Consequently, it must circulate several times more air to deliver the same amount of heat. It will do this with both increased flow (and static pressures) as well as longer cycles, probably continuous when it’s cold. This will dramatically exacerbate the tendency of leaking duct in an unconditioned space to force air-change.

      Conventional wisdom is that forced-air systems inherently reduce humidity. That’s not true. It is the associated duct leakage in unconditioned spaces that causes the problem. With all ductwork in the conditioned space, there is no problem.

      Some other things that may be causing or adding to your problem:

      The lower duct temperatures of the heat pump system may not allow the humidifier to achieve it’s rated output.
      The much increased air circulation may have contaminated the evaporator wick in the humidifier.
      The Infinity control has separate settings for heating humidity and cooling humidity..
      The humidifier may have a separate humidistat that is limiting it.

      My recommendation would be to have your home evaluated with a blower door and the ductwork tested with a duct-blaster. Some utilities will do this for free. Perhaps more important than the actual testing, is that the tester may be more knowledgeable about your problem with respect to air changes than your HVAC contractor.

      Good Luck, I see that you have posted on many forums.

      • Appreciate your adding to the discussion.

        Our utility does not do ductwork testing and neither does this contractor as I did ask if they did that prior to getting the system installed. However, in light of your input, I’m going to pursue this further as it might potentially lead to some cost savings on an already large electric bill.

        I have reinsulated the attic to and the basement to code levels, replaced some exterior doors but have not replaced the windows. The house was rated as being moderately tight after examination by several different contractors but in no way is it super tight.

        Again, I had not considered lower ductwork temps but that makes sense. As far as I am aware, the Carrier thermostat is controlling the settings of the humidifier, but will check with the contractor to ensure that no separate humidistat is interfering with that and governing the humidity output. Another good tip.


    • Here’s an afterthought. You’ve obviously spent a lot of time and probably money trying to solve this humidity issue. Consider buying a whole house console humidifier as a diagnostic tool. They cost about $200 and will output 5-6 gallons a day. You must fill the jugs daily, and as such you will know exactly how much water the system is putting into your home.

      If your humidity rises significantly, the problem is that the bypass humidifier isn’t doing the job, for whatever reason.

      If the humidity doesn’t shoot up after a few days, the problem is air leakage, probably in your ductwork.

  8. 5 yr old Trane 15xr. Heat Pump shuts down around 5 degrees, stays shut down until around 10 degrees, then starts on its own. This performance is very consistent. Installer thought it was the defrost board and replaced it last spring. Winter is back and it is doing the exact same thing. Installer says there is no cold override setting and the HP should always run. Other than this issue the HP is perfect, keeping a 2500 sa ft home comfortable with minimal electric strip backup. Any insight into what is going on here would be appreciated.

    • That sounds like a programmed behavior since it’s so consistent. And at those temperatures, most HPs would really be struggling.
      See if you can find a Trane factory rep to help you. Installers often aren’t familiar with the ins and outs of every model – even well informed ones.

    • Mike, here’s some more information that I located. It’s an installer’s manual for heat pumps and thermostats. There is a restricted mode mentioned that such a temperature so I suspect that this setting is what’s causing your system to shut down at low temperatures. I wouldn’t go changing this randomly because there’s probably a reason they have that setting, for example, at low temperatures the pressures may be out of range for the compressor. It’s another reason to contact the factory for their guidance. I wouldn’t want you to change anything that might damage your system.

      Good luck, hope you can figure this out. Sounds like your systems working like a champ in other respects.

      • T.D., Thanks for the input. My thoughts also. I’ll try quizzing Trane and keep you posted. Temps in the 20 – 30’s last few days and the issue has not repeated itself.

      • T.D., Had a service tech out today for routine preventive maintenance on the air handler. Trane authorized and I asked him about the 5 degrees cut off and 10 degrees restart on the HP. Answer: we put thermostats on some HP’ s at installation. You probably have one. Trane doesn’t do it out of the factory. Mystery solved – I hope.


  9. This is the best article I have ever read about heat pumps. So here in SC which does not have cold winters(few really cold days and nights a year) and a house that is 1740 sq ft, somewhere between a 2.5-3.0 ton heat pump should be the right size?? Of course, depends on the variables you mentioned. I do have one question. Last night it got down to 15 degrees here(unusually cold for SC) and I was told that a heat pump should still be able to get the temperature in the house up to 70 degrees. Is this true?? ANYONE can answer. Thanks again for the great article. Glad I found your site.

    • Richard, thanks for the nice comments.

      As for operational temperature, you would definitely be pushing it with most heat pumps to keep your house at 70F degrees when it’s 15F degrees out. On the other hand, people may have been referring to the heat pump along with its auxiliary heat strips or other backup heating system, would probably have no problem.

      Regarding sizing, like you said there a lot of variables. However, from what I’ve seen, a 3 ton heat pump in a well insulated house of your size, should do fairly well.

    • Sizing a heat pump requires that you have some idea of the heat loss associated with your house. That said, you can get a pretty good idea from your heating cost in previous years – on a poor, average, good scale, which is enough to get in the ballpark.

      15 degrees outdoor is an extreme for your climate. You should concentrate on sizing a system for the typical winter (/summer) and install staged electric backup to handle the rare extremes. Electric boost/backup is inexpensive to install, and the incremental cost to run on a few rare extreme days would be insignificant.

      But I think you are concentrating on the wrong end of the spectrum in sizing a system. Your A/C load is probably greater than your typical heating load. An inverter heat pump system like the Carrier Greenspeed will do a better job of air conditioning and rates at the top of the scale in efficiency.

      In the Northeast, NH and Massachusetts, we put a three ton unit with 9Kw backup in a well insulated (air sealed) home the size of yours. The electric backup typically runs to supplement the heat pump on a few cold mornings when it gets below 15 – 20. Three ton easily handles the A/C loads here.

  10. Hi I installed a Mitsubishi 18000 btu unit in an older home I have completely renoed using closed cell sprayfoam. Works great, last winter here in Nova Scotia was one of the coldest in 50 years and my total heating cost for the heating season was 1000 for a 1600 sq ft home. Only regret not upgrading the windows to casement or tilt and turn triple pane. Installed dual pane low e and argon single hung and they puke heat

  11. Part of our issue is that while we were SUPPOSED to have new thermal windows and insulated siding, that did not happen since my wife decided that she wanted to choose the style of window and color of siding. Net result…months of delay and no opportunity to install windows prior to winter. So we are heating a fairly inefficient structure. I think that this may be one of the major causes of the system having to work so hard to maintain heat in the low 20’s and teens. Anecdotal evidence from others who have the same Greenspeed system is that the system should work fine down into the high single digits. Again, assuming a tight house. I’ll let you know next winter what changing from 100 year old windows and ’70’s siding with no added insulation under it makes.

    Thanks for your input!

    • Phil – unfortunately, I think you hit the nail on the head. Heat pumps are quite sensitive to the building construction, which is why they got a bad rap in the past. With newer heat pumps, they’re more forgiving, but as you’re finding, they can do only so much. Your efforts to improve the windows and insulation should help things quite a bit.

      Now, as for that insulation under the siding, write again when the time comes and maybe we can help reduce wasted efforts there. 🙂

  12. Ted,
    We recently installed a Carrier Infinity Heat Pump with Greenspeed paired with a 97.5% efficient propane furnace. We live in west-central Illinois.

    Right now, we have the propane backup lockout set at 10° (as suggested by a Carrier rep). We’ve had a few days of 12-20° evenings so far and it seems as if the system is working pretty hard to keep up and has not reached the set point on our thermostat twice.

    2 Questions…

    1) Based on a system that might be running at full capacity and either just keeping up or falling short by a degree or two…would it make sense for me to raise the lockout temp by 5 degrees?

    2) When the back up system (propane) comes on, does the heat pump continue to operate as well? I’m hoping I’m not just shutting down the heat pump entirely but rather, adding propane heat to the mix.

    • That’s pretty nice performance but I’m not surprised that the system struggles in the teens. Most of the time, the system would be designed with a balance point between 25F-35F. I prefer the lower end of that range for my climate as it would allow it to run about 90% of the time on heat pump, just calling up the propane when it gets really nippy out.

      To answer your questions, you’ve proven that the lockout point is too low as it is, so I’d bump it up. All the theoretical calculations can’t outweigh the empirical evidence – your system can’t keep up with the heating requirements at that low a temperature.

      Because of the placement of the coils and the combustion chamber, the heat pump needs to turn off in most combined systems. I’m not intimately familiar with the exact configuration of the Carrier unit, but every combustion/heat pump system I’ve seen has the combustion heat the air before the air moves through the coils used for the heat pump. Because of the physics, the heat pump coils would not be able to impart any more energy to the air stream, so it shuts down. That’s why a low lockout temperature is desirable.

      Keep tweaking that lockout temperature until you get the heating you’re comfortable with. It’s a delicate balance between efficiency and comfort.

      • We installed a Carrier 25VNA inverter heat pump with a condensing propane furnace in a building last fall, and monitored it’s performance through the winter. We logged the power used and duct temperatures. The climate is northern New England (New Hampshire).

        The heat-pump supplied virtually all of the heat. It worked down to zero outdoor, and last winter it switched to propane on only three sub-zero mornings.

        Propane is very expensive. It’s hard to imagine any scenario above a COP of 2 where the propane would be more economical. So the crossover point is really a practical matter of heat pump capacity vs. building load. Hybrid gas/heat-pump makes more sense where natural gas is available. We now use multi-stage electric resistance boost/backup. The infinity controls know how to use it and unlike the furnace, can be used with the heat-pump to top it off on cold mornings. It’s inexpensive, costs about the same to operate as a propane furnace, and supplements rather than replaces the heat-pump in cold weather.

        It sounds as if your heat-pump may be a tad undersized if it’s not delivering enough heat at 10 degrees outdoor. It’s also possible that your duct work was sized for the furnace, and isn’t capable of delivering maximum heat from the heat pump because it requires significantly more air-flow due to the lower supply temperatures. You can tell if that’s the case on a cold morning because the infinity control will tell you if the heat-pump is working at 100% of capacity.

        If your climate is like ours, single digit outdoor temperatures are not a big part of the overall seasonal load. We factor them in using degree-hours rather than degree-days because that’s the typical case – A few cold hours in the morning. If it’s more of a factor, consider adding electric resistance to supplement, rather than replace, the heat-pump in those cold situations.

      • You make good points. My guess is that the installer may have sized the system conservatively since it had the propane backup. Even with an inverter system, you don’t want to dramatically oversize the unit, even though it’s much more forgiving.

        I do take issue with your claim that electric resistance backup heat is inexpensive compared to propane. This is totally dependent upon where you live. In Massachusetts, NY and elsewhere along the East coast, electricity is running $0.20/kWh, so running resistance heat is really expensive compared to all other fuels (again, depending upon fuel costs). Where I am in Pennsylvania, electricity is about $0.16/kWh and my last propane fill was at $1.85/gallon. So where I am, if the COP drops down to 2.0 and I’m using a condensing propane furnace, propane is less expensive than the heat pump. That’s $23.13/million BTUs for the heat pump and $21.40 for the propane system. Double the electric cost if you’re using electric resistance heat. So it absolutely makes sense to use propane at these fuel prices.

        Propane does fluctuate wildly, so some people pay $3-$4/gallon, at which point, I 100% agree with you.

  13. I need advice, again.
    Ok, I am still in the process of finding a heat/air dealer. I think I may have found one that seems honest. I have soooooo many quotes, and such big price differences. also one telling me I need this or that.

    So how does this sound, and is there any questions I should ask the dealer, or add onto what they have quoted me in this proposal.

    RHEEM 2 ton gas pack 14 seer.
    2 ton duct work.
    dampers tranklines.
    2 RRPL- B024JK0E

    small home, 820 SQ ft.

    • It’s definitely a daunting and confusing process. While I couldn’t say anything definitive, not being from your area etc., $10,000 for a full system install with ductwork sounds like a decent price.

      The main thing I’d want to be sure of is that there are no hidden costs. Are they guaranteeing that the system will be installed for that price or is there anything that could drive up the cost?
      And of course, there’s the warranty. Both the manufacturer’s equipment warranty and the installer’s.

      Another thing that’s always recommended is to check reference. Insist on three customer references and then actually call them and talk to them about their experiences.

  14. Hi, thank you again.
    Ok, I contacted Ga Power. they will come out and give free audits to their customers. I am waiting on them to call me and give me a date and time (usually 4 to 7 business days)

    I went to home depot today and bought some door kits to re-do my doors, and some caulking rope to seal the windows and a window kit (with the plastic film that uses hair dryer to make it fit tight. I am going to do everything in my power to get it tight. I know when I get my heating system they will insulate my attic and crawl space. and with the new ducts I should be well on my way.

    I have still not heard back from the big name that came yesterday, so I will write it off. maybe a blessing in disguise. I know I will find the right one. sooner or later.

    I am pretty set on the infinity line. I just think it will suit my needs. at a 15 or 16 seer.

    I hope I am making the right choice. funny thing… when that guy was here yesterday I ask him which unit would serve my needs better? he said he cant tell me that because he don;t live in my home. I said but you are the professional, I am seeking your professionalism to get me on the right track.
    He simply pushed the greenspeed.
    then went on to tell me trane was going out of business, or being sold. not to trust trane.

    Ok, again thank you for your time.
    wish me luck with my weather kit. ((:

    • Before you go rushing headlong into sealing your house tight, talk with that energy auditor. There are times when you want to be conservative with the approach. They should give you recommendations and priorities. This is important because you could spend a lot of time doing things that might not make much of a difference. I’m not saying that what you are planning is wrong, just hold off a little to hear what they have to say.

      The Infinity units are good quality. The final outcome will be dependent upon the skills of the installer. Make sure that whomever you have do the work has a long track record and skilled employees. Ask about their employee training and certification. The better companies will have all their technicians NATE certified. While being certified doesn’t guarantee anything, it at least shows some level of commitment to training. If the salesperson tries to downplay certification, that usually means they’re not certified and is a red flag. There are a lot of “yahoos” out there who call themselves HVAC technicians but really don’t have the skills so you have to be careful. Again, Angie’s List is a good way of finding the best people in your area.

      • Be sure that the Carrier people are talking about the 25VNA series inverter heat pumps if you want the best performance. The two speed Infinity units can turn in SEER values like you are quoting, but they are not as adaptive to the inverter heat pumps. That’s what distinguishes the Greenspeed line line from competitors like Trane.

        The inverter technology allows the control to run the compressor at any speed, and they control the expansion valve to optimize the pressures and temperatures in the heat pump cycle to the outdoor and indoor temperatures. That’s exactly the reason that the popular mini-splits are so efficient.

        The best efficiencies are also linked to using a carrier ECM air-handler which will allow the control to select one of, I think five, speeds to get the appropriate air flow for the load as well.

        All that means that the system can do it’s job better. There was a humidity problem mentioned. An oversized AC unit will not be as effective in managing summer humidity as a correctly sized unit, and the size required changes with the conditions from hour to hour. With the inverter unit, the capacity of the unit is continuously adjusted to match the load. So the unit can longer at a lower capacity to remove more latent heat (humidity).

        In the winter, the same is true that the unit will deliver lower continuous heat, rather than cycle on and off resulting in a temperature roller coaster. In Atlanta, a simple inexpensive three stage electric auxiliary heating board is all that you will need.

        I don’t sell or install these things, but I’ve recommended them and have had success in New Hampshire winters (and summers). Get that audit likeTed recommends, and see if the auditor can recommend someone to do a manual J or otherwise reasonable assessment of the load and capacity requirement. Installers always oversize.

      • This is all true – the true variable speed systems are excellent in their ability to adapt to various conditions. However, for such a small home, a two stage heat pump should be more than adequate for the money. The inverter drive systems are so much more expensive in most areas that it’s just impossible to justify the added expense. On the other hand, if one can be had for a reasonable price, then it’s certainly worth it.

      • Within the Carrier line, the distinction is in the outdoor unit only. The 25VNA has a cost of a couple thousand more than the two speed. The rest – ductwork, AHU, infinity control, installation, are the same. So I would take a hard look at the numbers and evaluate the lost opportunity of not popping for the upgrade.

        In a perfect world, a good two speed would be correctly sized and perform well most of the time. In this case, I’m hearing that the sharks are circling. The easiest way to get more $$$ out of a sales opportunity is to oversize. The other incentive for an installer to oversize is that the downside of oversizing, from a business perspective, is much less than that of undersizing. If they are not competent and/or use rules of thumb to size the system and add fudge factors at every step of the way, you can end up with AC that has a duty cycle of 25% or less in moderate conditions. In Altanta, that won’t deal with the humidity as well.

        So I see the 25VNA as not only a more efficient system, but something that will be more forgiving of shortcomings of the designers/installers. All for a couple thousand more.

        Now if the conversation is 25VNA vs. Mini-split or multi-split, those arguments go away. They are functionally equal with respect to adaptation to load.

  15. Hi.
    I read your page, got good info. thank you for giving great advice.
    I have a problem, a big problem

    My stats:
    850 sq ft home.
    2 bedroom, 2 bath. (at this moment- no heat or air) so we will be starting from scratch.
    Atlanta, Ga area.
    I want a heatpump. but like many others, am afraid the winters here in Ga wont heat my home.
    I have read that GREENSPEED is the BEST? (I will be getting all new insulation/ducts/ and crawlspace insulated.

    Is it worth it for me to get the greenspeed alone? or would I need duel fuel?
    I am really frustrated now. seems all the big name heating/air folks in Atlanta are telling me different things, with huge prices.

    any advice is greatly appreciated.
    Thank you.
    Ms. G

    • Atlanta should be a great climate for heat pumps. They work pretty well all the way here in Pennsylvania and typically, anything from the Carolinas and south is considered a good for heat pumps as long as they are sized appropriately. Since you have hot summers, the balance of heating and cooling loads on the heat pump and air conditioning is much better than northern climates where there is much more heating than cooling. This allows the system to run more optimally during summer and winter.
      Since your average LOW temperature in January is 34F, a properly sized system will likely have to almost never use backup heat, which is excellent because most modern heat pumps are very efficient.
      With the size of your home and the measures you are taking to insulate and weatherize, a Greenspeed may be overkill. I’m all for using the latest and greatest technology, but sometimes it just doesn’t pay. Around here, that system costs upwards of $20,000 without additional ductwork etc. and the additional efficiency will never pay for itself. Your house would likely use one of the smallest heat pumps, probably two or two and a half tons but a professional would have to evaluate and properly size the system to your home.But again, I’ve helped people up here with homes larger than yours and they got by with a 2 1/2 ton system so I can’t imagine needing more for your home.
      As for the technology, you’d be most comfortable over the widest range of temperatures with a Greenspeed since it has variable speeds but a two-stage heat pump should be great also. Frankly, even a basic, single speed heat pump would probably work well.
      For backup heat (which may be required by building codes) electric or gas/propane should be fine in your area. Honestly though, if I lived in a climate like yours, I would just use inexpensive (to install) electric backup heat. The system should be sized large enough to supply your heat down to at least 35F with ONLY heat pump output, so that expensive (to run) electric backup heat should be locked out to only come on below that temperature, which for you would be pretty rare.

      Hope that helps. If they try to confuse you, feel free to bounce what they’re telling you off of me. I’m happy to throw in my two cents!

      • Hi and thank you for replying to me. I am soooooo confused now. I have had several companies come out and measure and count ducts and on and on. they are all telling me different things and what I need. like today the big name company told me about the greenspeed. this is the second company that told me I need that. I am in a sorta a strange situation. ex is paying for the install of the new unit on whatever I get. so money is not the issue here. but it will be me to keep up the monthly utility bills. so I want something good, and very efficient. right now my house has NO heat or air. been like that since 2004. use to have gas heat. but the furnace went out, and couldn’t be repaired. so we were using little electric space heaters.

        I wanted a heat pump for the benefit of having heat and air. but was told in the winter a heat pump wont heat my home,, I have tried to research it. but again even on some forums I am being told this and that. and the big name dealers that have come to my home are telling me this and that too.

        I want at least a 15 or 16 seer on whatever I get. I am scared of gas heat. but if that what it takes, so be it. I have been freezing every winter and am tired of being cold.
        as I said. ex will be footing the cost of the unit I get and all the labour/insulation and so fourth. my problem is I just simply don’t know what to do/decide on or what will fit my needs. I want the ‘best’ but not over the top. I don’t need bells and whistles. but I really want efficiency. I so wish we had some honest dealers here in Atlanta. I have had several BIG names in my home, and they all tell me something different. I looked on the website and see the infinity heat pumps are nice? at a 15 or 16 seer, would that benefit me at all? I was told if I go with that one, I would need a back-up of gas heat as well. which I don’t wanna have to do.

        I really appreciate your help. (wish the folks in person were as nice as the folks online that have been trying to help me out. (one guy told me to get a trane furnace- gave me stats and everything. when I presented what I wanted today to the heating dealer, he knocked it right down. told me trane was being sold and on shaky ground right now.

        please advise me further.
        Thank you.

      • which one of these would be good for me? if any?

        Infinity® 15 Packaged Heat Pump System 50XT-A
        Performance™ 14 Packaged Heat Pump System 50VT-A

        my entire house has mould due to heavy humidity I really need something to take care of that.
        again, thank you.

      • Wow, that sounds confusing indeed! Your situation is exactly why I started doing energy consulting years ago – people need an independent person they can count on for an honest evaluation.
        If you’ve been living without heating and cooling for that long then anything will be an improvement. But we’ll get you pointed in the right direction. There has to be someone in your area who will deal with you straight. It sounds like they all see $$$ because your ex is paying for the system.
        You really want someone local you can trust because there’s only so much advice I can give from here. I will tell you, definitely, a heat pump will work fine in Atlanta all year round. Like I said, they work fine in much colder climates, so any contractor that tells you that a heat pump won’t work in Atlanta is either incompetent or is a thief trying to up-sell you. In either case, you should cross them off your list! People like that really make me angry.

        Here’s my recommendation – join Angie’s List. Then, fine a good, independent energy auditor come in and evaluate your home and make recommendations. This will cost $300-$500 but it will save you much more than that in the long run and they’ll be able to help you find an honest contractor. When you’re looking for an energy auditor, pick someone who doesn’t sell heating systems – you want someone who can give you unbiased recommendations.

        They’ll make recommendations on how to insulate and air seal your home and should be able to suggest a company to do that work. This work before the heating system is some of the most important because an inefficient home makes a heat pump work much harder. Then, they should be able to suggests options for your heating/cooling system and even evaluate the quotes that the contractors give you. I used to do that for my clients which helped them filter out the riff-raff!

        Best of luck.

  16. Now, perhaps the bigger question for consumers like me…selection of equipment. Assuming the same contractor and same SEER values, same warranties, comparable prices, how does a consumer discern what equipment is best? The closest thing I’ve seen is a Consumer Reports graph on heat pump repair histories. Do I need to go to the specs of each manufactuer’s model, and if so, how many variables should I narrow the search down to, and what are they?

  17. I agree with Ted on the heating side, though that doesn’t seem like it has the potential to be a huge problem in heating season. But in case you’re talking about warm days in the winter with low outside humidity, it’s important to recognize that the dehumidification is a self-correcting system. That is to say that with a dry bulb of 75, the dew point is 55 degrees at 40% RH and about 42 at 30% RH. So the system wil naturally slow the removal of water below 40% and pretty much stop altogether by 30%. The evaporator will actually maintain a higher temperature at low speed and thus stop dehumidifying at a higher RH.

  18. On the humidity levels and comfort, it is nice to be able to lower the humidity level inside the house to maintain, say 40%-50%, but in the winter, if one is not watching what they’re doing with the VS, the humidity level could lower to uncomfortable ranges, even in Florida. So I guess I would run the unit at full speed to safeguard against over-drying conditions in winter.

    • I’m sorry Mike, that doesn’t make any sense. Air conditioners dehumidify the air by lowering the temperature of the coils below the dew point. This forces the water vapor in the air to become liquid water that condenses on the coils then drains out of the system.

      In a properly installed heating system, there is zero dehumidification of the air. HOWEVER, in leaky forced air systems, where you’re losing house air to the outside (often through the attic) or sucking in outside air (again through leaky ducts) then the low humidity outdoor air replaces the normal humidity air in the house, leading to dry conditions. This is the primary reason people complain of dry air during the winter.

      • Let me try to state it another way, in the winter, the outside air is less humid, and when the heat pump is on, it tends to dry the air out even more (outside RH of 45% and inside somewhere in the 30’s) leading to that dry feeling. So my question I guess is will the VS worsen that issue, or can I set it to give me higher indoor RH than a fixed speed?

  19. Hey Ted, got a question for you. Let’s say you are being quoted two new heat pumps, both identical (same manufacturer, same outdoor and indoor unit, same SEER, etc) except one is a fixed speed and the other is a variable speed. If the fixed speed costs me, say $600 a year in electricity to operate, how much would the variabel speed cost? Thanks.

    • Hey Mike, this sounds like a question from Car Talk!

      First, there are too many unknown variables to give you any reliable projection of dollars saved. With that disclaimer, let’s dive in…
      The single speed motor is called a PSC (permanent split capacitor) motor. These have been replaced by an ECM (electronically commutated motor) in a variable speed air handler.

      The ECM motor allows the system to efficiently vary the speed of the air handler. It also monitors the electrical load placed on the motor which is directly related to the amount of air that the fan moves. The PSC motor in contrast, just runs. It doesn’t care whether your filter is clogged or all the vents are closed, it just runs. So to start with, the ECM motor allows a more optimal, automatic, selection of speed of the fan.

      In addition, the typical PSC motor is controlled using an inefficient method of speed control. So if you slow it down, you don’t save a proportionately lower amount of energy. Think of those old box fans with “low-medium-high” settings.

      Here’s a great blurb about the ECM motor and it’s efficiency.

      The critical number here is “Watts per CFM” – that is, how many Watts are needed to move one cubic foot of air per minute. This varies depending upon the speed of the fan, but let’s look at an “optimal” figure – for the PSC motor, you’re looking at about 0.55 W/CFM for a larger one, and as low as 0.33 W/CFM with a smaller one. In contrast, the ECM uses about 0.17 W/CFM (compared to the 0.55 for the PSC) at a modest air speed used in a small heat pump (around 750 CFM).

      BUT, BUT – the numbers aren’t as rosy when moving lots of air like in a 4 or 5-ton heat pump. In these cases, you might have a blower moving 1900 CFM. In this case, the PSC motor uses about 0.42 W/CFM while the ECM motor uses 0.36 W/CFM. While still significant, it’s nowhere near as dramatic.

      For a financial analysis, you can see that it can vary quite a bit. However, let’s just think about a “typical case”. Looking at the graphs, if you’ve got an air handler moving 1200 CFM, the PSC uses about 0.40 W/CFM and the ECM is around 18 W/CFM. Let’s say 50% savings as a round number.

      You mention $600/year to operate. That’s $600 to run the entire system, not just the air handler. Based on my own personal measurements, my ECM air handler for a 4-ton system uses about 10-15% of the total, so let’s say 15% of the $600 = $90.

      If I had been using a PSC that number would have been somewhere between $150-$180, for a saving of $60-$90/year.

      These are really “back of the envelope” figures, but should give you some idea of the savings. There’s other factors that come into play in real life, but this should give you a starting point.

      • Check that out, your kung-fu is strong Ted :)! Thanks for the reply. Here’s a bit more background. I live in Florida, and am about to replace my 3 ton (3.5 ton air handler) 8 SEER heat pump with a 16 SEER, so I should automatically cut my h/c annual electricity costs down from an approximated $1200 to $600. I have a couple quotes for $5,500 for a single speed builder’s grade model. I was also quoted about $6500 for a same SEER variable speed/2 stage compressor heat pump system that I guess would be considered a mid-line quality series. Hence the question about how much more electricity cost saving I would see with the variable speed stuff. I’m guessing for my application, about $100 per year, making the payback to spend the additional $1,000 about 10 years. So if there are dollars to be saved, why doesn’t the SEER number reflect it?

      • Aha, now you’re really comparing apples and oranges. I almost always recommend going with the two-stage heat pumps/air conditioners. Both for efficiency and comfort. In muggy climates, running “slow and long” makes for a much more comfortable house than the single speed, single stage system that just bangs on full blast. In addition, the first stage will be quieter, you may not even hear it running from inside. For me, the two-stage variable is a no-brainer at $1,000 price differential. That sounds like a good deal.

        As for the SEER numbers, I think they’d argue that that would complicate testing because then you’d have to test all permutations of air handler and compressor. So generally, I believe they still ignore the air handler in the equation. OTOH, the two-stages are included in the equation, and is largely how they achieve the higher efficiency – they figure that the system will run some percentage of the time in stage 1 and the rest at stage 2. This of course depends on climate, so the SEER rating will vary. This also applies to winter heating needs. In mild climates, you may never have to heat using stage 2, so the system can run very efficiently and deliver a more uniform temperature to your home since the air handler will run longer.

        Lots of interacting variables but ultimately – two-stage, variable speed is more comfortable and efficient than old-style single-stage, single speed.

      • I was trying to compare granny smith apples to macintosh apples :). So I guess the extra $1,000 or so would pay for itself with electricity savings over its life, would probably have ‘better’ components, and be quieter and offer more convenience huh? Sound about right? Still have a couple questions for you.

      • One of the things not being mentioned here is latent heating load. I’m from New England, so that’s not as big a deal, but in Florida, it can be the whole ball game. A two speed (or better an inverter system) will run longer to achieve the same sensible temperature (say 75 degrees), and in the process will remove a lot more water thus lowering the humidity. Condensing water vapor releases A LOT of heat, and thus increases the load on the system – even though it isn’t doing anything to reduce the sensible temperature of the air. So the difference between the two systems is that they both will lower the air temperature to the same value, but the two speed will typically also maintain a lower humidity. It’s a benefit not reflected in the SEER standard.

  20. Hi Ted,
    I live in South Jersey and am having a 1 1/2 story 2100 sq ft. custom modular home built (2×6 walls R-21, ceilings R-38). The half story ( media room & guest suite) is 525 sq ft. and will be it’s own zone. Natural gas may or may not be extended to our street. We are considering the Carrier Infinity Greenspeed 59MN7080 fully modulating 97% furnace (run on propane for now) with a 25VNA048 4 ton variable speed outdoor heat pump (SEER 19, EER13.3, HSPF 12.) with touch screen wifi wall controller for downstairs and a Smart Sensor for the second floor. Does this sizing sound right? Cost including duct work $29,550.

    Our other option is a 3 vertical closed loop geothermal system for $34,650 after Federal Tax Credit.

    I’m a bit out of my element here; it is all way more expensive than I thought it would be.
    I like the climate control aspect of the Infinity Greenspeed system but I’ve always thought geothermal was more energy efficient. What in your opinion would be a better bet for overall cost, energy efficiency, and comfort?

    • In a new home of the size you’re building, that sizing sounds roughly appropriate. However, the only way to really project the size is to do a full energy model that takes into account windows, walls, insulation levels, home orientation etc. A reputable HVAC installer will want to do this using what’s called a “Manual-J”.
      I really like the concept of the Greenspeed which should be much better over a wider range than conventional heat pumps. Combined with gas/propane as backup for really cold days, you’d be in great shape. The quoted pricing, including ductwork, sounds in-line.

      Geothermal can be great. I’ve got one and it’s worked well for me. With a properly sized and installed geothermal system, you should be able to squeeze out even better performance and efficiency than the Greenspeed. Each has its relative advantages/disadvantages. In roughest terms, you’ll find that the Greenspeed heat pump will require less maintenance than the geothermal. Why? Because (conventional) geothermal requires circulating fluid through the ground loops. This has to be periodically checked and the pumps are another point of failure. While you can go years without problems, I tend to prefer the simplest possible configuration because I’m lazy – the more maintenance, the greater the chance for problems.

      On the other hand, the geothermal should provide more uniform heat output whereas the Greenspeed will have reduced heat at colder outdoor temperatures. However, with the Greenspeed compressor, it should be better than most other heat pumps. But, during the summer, the Greenspeed will be better able to provide high comfort than the geothermal. This will come as heresy to geothermal advocates, but the physics back me up. With the variable speed compressor, the Greenspeed can turn down the cooling. With the geothermal, even a two-stage geothermal, you simply can’t back off on the air conditioning enough to satisfy the moderate air conditioning requirements of our area. I know this from personal experience. My geothermal is great it it’s 90 degrees out but not if it’s 80 and humid, which is most of the summer around here.

      So there’s no perfect answer. If it were my house, knowing what I do now, I’d go with the Greenspeed.

      Hope that helps!

    • Hi Janice,

      This past winter I was involved in a project where we installed a 3 ton Carrier Greenspeed HP into a high performance 2500 sq ft building. Without getting into too much detail, it was a retrofit into an existing Carrier propane fired system with conventional A/C. The result is that in the three months Dec-Feb the heat pump worked great and used 2,308 Kwh.

      Did I mention that the unit is in central New Hampshire. I have data recorders on the system and it only used propane on three sub-zero mornings in January, as well as a small amount to aid in defrosting (a regular and normal part of heat pump heating). If I were putting this system in new, I would skip the gas furnace and install a three stage electric resistance supplement with a standard air-handler. The infinity control will recognize and use the resistance to boost any low output of the HP during high demand.

      I agree with Ted that the inverter technology does a much better job of matching equipment to load, especially in the shoulder months and during the cooling season. I think that by eliminating the gas furnace, you can get the up-front cost down considerably without sacrificing capability or economy. Last fall Carrier had a rebate program where they were throwing in the air handler with the 25VNA. Make sure you are getting the benefit any such deals.

      As an aside, the R values of the walls and roof are OK but not great. There are modular companies that are offering better shells, and in particular I’d be more careful to insure that the house will have low air infiltration, particularly with the 1/2 story where typically sloped ceilings and knee walls provide lots of opportunity for leaks. Ted has a blog post about how hard it is to fix those things. It’s much easier to get it right in the first place. Talk to your builder and get a contractual commitment on a good HERS rating and have a third party rate it after completion.

    • Hi Janice,

      This past winter I was involved in a project where we installed a 3 ton Carrier Greenspeed HP into a high performance 2500 sq ft building. Without getting into too much detail, it was a retrofit into an existing Carrier propane fired system with conventional A/C. The result is that in the three months Dec-Feb the heat pump worked great and used 2,308 Kwh.

      Did I mention that the unit is in central New Hampshire. I have data recorders on the system and it only used propane on three sub-zero mornings in January, as well as a small amount to aid in defrosting (a regular and normal part of heat pump heating). If I were putting this system in new, I would skip the gas furnace and install a three stage electric resistance supplement with a standard air-handler. The infinity control will recognize and use the resistance to boost any low output of the HP during high demand.

      I agree with Ted that the inverter technology does a much better job of matching equipment to load, especially in the shoulder months and during the cooling season. I think that by eliminating the gas furnace, you can get the up-front cost down considerably without sacrificing capability or economy. Last fall Carrier had a rebate program where they were throwing in the air handler with the 25VNA. Make sure you are getting the benefit any such deals.

      As an aside, the R values of the walls and roof are OK but not great. There are modular companies that are offering better shells, and in particular I’d be more careful to insure that the house will have low air infiltration, particularly with the 1/2 story where typically sloped ceilings and knee walls provide lots of opportunity for leaks. Ted has a blog post about how hard it is to fix those things. It’s much easier to get it right in the first place. Talk to your builder and get a contractual commitment on a good HERS rating and have a third party rate it after completion.

      • This is great news and advice – thanks for chiming in!
        When my geothermal goes, I’ll definitely have the Greenspeed on the top of my short-list.
        I agree with your suggestion – if you can get a 3-stage electric backup that’s controlled intelligently, it should work great. I’ve often tried to get people to install such systems but local HVAC companies balk and just install a single 20kW backup system that comes on at 35F-40F, defeating the purpose of the heat pump 😦
        Thanks again for your input.

      • With the fairly recent advances in air-source, their life cycle costs in many climates are probably better than ground source systems because of the cost of putting in the well or ground loops. But unless the failure is in the loop or well, I’d take a closer look in the advances in the ground source pump before switching to air source. Water Furnace is advertising an inverter ground source unit. The GSHP doesn’t lose capacity or lower COP in really cold weather, which is a big plus and should translate to better economy. The inverter water source units are probably expensive, but the Greenspeed is pretty pricey too.

        In a previous post you said you grew up “across the bay” from Marthas Vinyard. Are you talking Buzzards Bay – like New Bedford? I’m originally from Fall River.

      • True again. What I found in my financial analysis was that the investment return is shifting further up – the greater the use, the more effective it is to go with a ground source heat pump. With modest, well insulated homes, the use can be so low as to make the GSHP a poor investment while with larger homes and industrial applications, it becomes a “no brainer”. Of course, all this depends on fuel costs and projections too.

        I’m from even closer to MV – Woods Hole. Just a stone’s throw away.

  21. Ted, I have a 1100 sf house in rural MI where we have the worst of both worlds (cold and dry winters and then hot and humid summers). I presently have an old forced air propane-fired furnace which I know is not efficient. I’m considering taking it out of service and installing a split-unit heat pump and am very interested in your opinion. Note: just sealed up the house with new thermopane windows, added roof insulation and new, tight-fitting doors so think that I have the winterizing issues addressed. Question is: is my choice of a split-unit heat pump a wise idea in an area where winter temperatures can be below zero frequently?

  22. Another point to keep in mind with minimizing electric backup heat with a heat pump is to take advantage of (some) thermostats’ “anticipate” mode if you program a temperature set back for the nite. When the thermostat calls for heat in the morning it will use the heat pump exclusively to hit the target temperature. If you shut the system completely off overnight and then turn it on in the AM the thermostat will call for backup heat as well.
    We have a Honeywell 8100 and it was a couple of years before I figured this out! It will save money$ – in our area with 8 cents/kWhr juice it can result in savings of $10-$20 per month. We have 15 kW strip heaters – or $1.20 per hour if all strips are running.
    Likewise, bumping up the temperature set point more than one degree usually forces the backup heat on. So it’s nice if everyone in the house can agree on one temp and keep it there.

  23. Ted, Got onto your blog after googling the Fujitsu 12RLS. This winter we are using a Daikin 12MBtu Quaternity system. We’re in 7,000 DD New Hampshire. Last winter we burned 1.5 cords of wood and 500 gallons of oil. So far this (mild) winter we are burning less wood and have used 60 gallons of oil. The reason I’m looking at the Fujitsu is that I’m considering a second mini-split to virtually eliminate the wood and remaining oil.

    We’ve found that the core of the house heated by the mini-split is more comfortable with constant temperatures and the unit is quieter than the refrigerator. We will still probably use the woodstove on the dozen or so evenings where it’s single digits outside, and the oil will still be available to heat the guest bedrooms that are usually closed off.

    I’m completely sold on the air source technology and can’t imagine spending money to dig a well or bury ground source pipes, at least in my climate.

    I got the inspiration for using mini-split from this guy: http://www.thrivingonlowcarbon.typepad.com/
    Take a look. I see that you subscribe to Building Science’s information, Marc has been doing it about as long with the same approach.

    • Hey, thanks for a link to that blog. I grew up across the bay from Martha’s Vineyard, so I’ll have to check it out!

      It sounds like you’ve had great success with your mini-splits. That’s awesome.
      From what I can tell, the Daikin and Fujitsu units are almost identical, so if you’ve had good luck with the Diakin, I’d stick with it.
      Thanks for sharing your experience. Some people don’t believe these new air source heat pumps can be so good, but I’m sold on them too. They’re incredible.

      • Take a look at the new Carrier GreenSpeed 25VNA series heat pumps: http://www.carriergreenspeed.com/wp-content/uploads/2011/07/25VNA-Product-Data.pdf
        These can be installed in ducted environments and have COPs and low-temp performance comparable to the mini-splits. Like the mini splits, they are inverter controlled. Some losses possible due to ducting, but otherwise a good solution, especially when paired with a high efficiency gas furnace as an air handler. The Infinity control system allows setting the outside temp crossover point, so the system will switch to gas at what I figure to be about 5-10 deg F in my neighborhood of if Y2 heat is needed. I’m not pushing Carrier, but they seem to be a little ahead of the pack on this.

      • Thanks for the note. I just checked this out yesterday and they look very impressive. If I ever have to replace my ground source heat pump, I’ll go with something like that!

  24. Hello Ted, thanks for that infomation. I’ve read the 12RLS manual carefully and I can see no reference to “back up” heating provision for that unit and the interior air handler had nothing to indicate that “back up” heating is being employed. Am I right in guessing that the 12RLS has no back up heating?
    On another issue, when my unit was installed last month the installers used what I would guess is the standard neoprene pipe wrap which comes with the unit. I noticed that down at the cutout where the pipes connenct to the outdoor unit there was a connection on the “hot” input and about 1/2 inch of return pipe not covered with insulation so I just stuffed some fiberglas insulation into that cavity. I recognize that is only a tempory fix as the fiberglas will get wet eventually.
    Should I increase the the amount of insulation on the input and return pipes and what should I use?
    Best regards


    • Yep – no backup for these units. I think they’re often paired with electric baseboard heaters that are only used as-needed.
      As for insulation, I’d certainly want to see all of it covered, but if it’s just a 1/2″, I wouldn’t worry too much. I’m pretty anal with mine though, so I don’t like seeing any copper showing 🙂

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s