Why can’t they make a thermostat that can keep the house at a constant temperature?

Someone asked me this question, and I live this reality every day. Let’s look at what’s involved!

Each room in the house has its own thermal loss and gain. To simplify, this is directly related to the difference between the indoor and outdoor temperatures. This is mostly true but other effects like sun shining, people, electronic devices etc. all affect the equation. But for now, think of each room as a thermally insulated box losing a certain amount of energy over time when it’s cold out (this discussion applies to air conditioning also, just in reverse).

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Is Geothermal Worth It?

On paper, geothermal, or more accurately, Ground Source Heat Pumps (GSHP), are amazing. They pump out endless heat during the winter and cold during the summer at costs that are often much lower than conventional heat pumps. They don’t pollute (directly). They’re quiet, comfortable and, when properly maintained, should last decades.

But what’s the reality? Are geothermal heat pumps really worth it? Keep reading to learn the answers!

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What are the biggest electricity consumers in a typical home?

As a baseline, consider that typical homes in the United States consume on average 30–60 kilo-Watt-hours (kWh) of electricity per day (=900–1800 kWh per month) at a cost of $0.10-$0.20 per kWh. Those running on electric heat often double these numbers.

  • In homes with electric heat, the heater can dominate all other electric consumers. Heat pumps, while considerably more efficient (1/3 – 1/2 the consumption) than straight electric resistance heat (like an electric baseboard heater) still consume substantial amounts of electricity. Consider that a typical heat pump system uses 3kW – 6kW while running, daily consumption in cold days can easily be 30–60kWh or more. This is why home insulation and air-tightness is such an important way of conserving energy. Same is true if the home is heated with oil, gas or propane – home heating and cooling costs dominate all others, so a tight, well insulated home pays dividends year after year.
  • Electric water heater – consumption varies drastically depending on a family size and hot-water usage. But an average is about 400 kWh per month. A modern heat-pump water heater can cut this in half.
  • Refrigerator/freezer – older units were much less efficient than a modern, EnergyStar unit. A typical range is 40–80 kWh/month.
  • Lighting – with the advent of energy efficient LED lights, this has shifted considerably. A home that has the equivalent of ten, 100W bulbs running 12 hours/day uses 12kWh per day or 360kWh/month. If all those bulbs were replaced by 14W LED bulbs that put out the same amount of light, that would be reduced to 1.7kWh/day or 50kWh/month. Lighting is an area where every home can dramatically reduce consumption by replacing conventional bulbs with LED in high use locations like the kitchen and living rooms.
  • Air conditioner – central air conditioners and their blowers consume from 3–7 kilo-Watt-hours (kWh) per hour of operation.
  • Home electronics – computers, DVRs, TV, stereos all add to a home’s use and together add up to 200W-1000W/hour, every hour. Typical consumption is 4–10kWh/day or 120–300kWh/month.
  • Cooking – electric ranges and ovens consume 2kW–4kW while running and might be operated for an hour or two per day on average.

Other items that add considerably to electric bills but are less common:

  • Pool pumps – most are drastically oversized and run 12 hours a day. A typical pump uses 2500W, so that’s 30kWh/day or 900 kWh/month! Replacing that with a two-speed or variable speed pump can cut this by 75% – well worth the investment.
  • Spas/Hot tubs – outdoor hot tubs use about 6–15kWh/day, depending on usage, design and temperature, call it 10kWh on average. That’s 300kWh/month. Since many people don’t use their tubs during the winter, it pays to shut it down for the winter, saving about $50/month.
  • Ponds – ponds have become very popular in the suburbs but most people don’t realize how much they cost to run. Those waterfalls require larger pumps, consuming 500W–1000W while a basic pond filter pump might use 100W-250W. Consider an average of 500W for 24 hours is 12kWh per day or 360kWh/month.

It’s extremely educational to install a whole-house energy monitor or use an inexpensive plug-in energy monitor to see how much energy each of your devices consume. But watch out, once you do, you may turn into a true energy geek, like me 🙂

What Temperature Should I Set the Thermostat to When Away for the Winter?

I recently received this question on Quora and decided to share the answer with readers there as well as on TedsTips. I hope this will save some of you from heartbreak after your winter vacation!

A primary consideration in cold climates is pipes freezing. It is very important to realize that pipes can freeze even if the home temperature is above freezing due to the locations of the pipes. I once owned a townhouse where the pipes would freeze when the outside temperatures dipped into the single digits outside, even though we were warm inside the house. How? The pipes ran up through an inside wall, across the ceiling and over to an outside wall spigot. The inside wall, at the top, opened to the cold attic, so that cold air would get into the wall cavity and freeze the pipes. This was fixed by air sealing the top of that wall cavity, but required considerable detective work to figure out. The pipes running through the outer wall down to the spigot would freeze near the spigot where the pipes were exposed to cold temperature, so this run had to be isolated from the rest of the house plumbing and drained during the winter.

These are two examples, that show potential issues that are made worse by turning down the temperature while you are away. Imagine the situation where the pipes don’t freeze when the house is occupied and the walls are warm enough to keep the pipes from freezing. Now, imagine reducing the indoor temperature, maybe only a few degrees, but enough that the cold from the outside overwhelms the meager heat coming from the house that is able to reach the pipes. This has bitten many a homeowner during winter absences.

Unfortunately, there is really no way of knowing if this will happen until it happens. This is why it is critical that you turn off the main water valve for the water supply to your spigots in your house when you travel*. The pipes may still burst, but at least your house won’t flood. When you return after winter and turn the water back on, you’ll know quickly that there’s a leak and can turn off the water and fix the leak before catastrophic damage is done. This is no exaggeration – I was called into a home that was literally FILLED with mold and had to be gutted. A pipe had burst and the owner returned after a month to find the house completely flooded.

*I was reminded (see comment below article) that you MUST NOT turn off the make-up water supply if you have a boiler for heating your home. This is very important. Boilers need available water to maintain system pressure in your radiators etc. Without make-up water, the pressure in the system can drop and the system will stop functioning.

If you plan on leaving your home for an extended period, it is always a good idea to have your HVAC company give the heating system a once-over to ensure that it is in good working order. While there, they can advise you on which water valve you can safely turn off and which you should not touch. It would be advisable to label all the valves for future reference.

Flooding is the most damaging effect, but there’s another, more insidious issue that can arise during winter house shutdowns – condensation damage and mold.

Water and Ice on a Cold Window

Condensation can lead to mold and wood rot

In order to understand this, I have to touch on the physics of condensation. Condensation is the conversion of water vapor to liquid water that occurs at or below what is called the “dew point.” At normal temperatures (say 70F), condensation rarely occurs during the winter because the home humidity level is modest and most of the inside of the home is above the dew point. However, even with typical indoor humidity levels, you can experience condensation on windows, because windows get much colder than the insulated walls of the house. You might have noticed this if you have curtains or insulating blinds. These help keep your room warmer but allow the windows to get even colder because they intentionally reduce the windows sapping heat from the room. When you open the curtains, you might find the windows soaking wet from all the condensation. Worse, the wood around the window, especially at the bottom edge, might be saturated with water.

Under normal circumstances, you would see this in the morning and could dry off the wood and allow it to warm up when you open the curtains. But when you are away, even if you don’t turn down the thermostat, the water will remain and can get worse every day. Over time, this will likely lead to mold growth and if allowed long enough will rot out the wood. For this reason, I highly recommend that people leave their curtains and insulating shades “UP” or “OPEN” when they are away for extended periods. You want to minimize the chance of condensation buildup and the associated potential for mold and wood rot.

Let’s continue this thought experiment. If you turn down the thermostat enough, the inner surfaces of your house (walls etc.) can get to a temperature below the dew point and, just like those windows, the water vapor in the air can condense on those surfaces. Many people have made this mistake and come home to a horrible, moldy mess! For this reason, it is extremely important to do two things:

1 – do not turn down the heat excessively. It’s impossible to tell exactly what temperature is too low, but in most climates, people find 55F-60F is safest.

2 – make sure you don’t add any moisture to the air while you are gone. This can be disastrous. For example, many homes have central humidifiers built right into the heaters. If you leave this one it raises the humidity level inside the house every time the furnace runs, likely leading to moisture problems. Turn off all humidifiers before you leave!

Even if you don’t have humidifiers, natural ground moisture can seep into the house through the basement, crawlspaces, etc. This is especially common in homes with dirt floors underneath. Water vapor rises up into the house, driving up the humidity. If you live in such a home, it is really important that you monitor the humidity levels in the home to ensure that they are not too high. During winter, indoor humidity levels will naturally be low, typically less than 50% relative humidity. Humidity levels above 70% are considered too high as they promote mold growth. Get yourself a humidity monitor (they’re cheap on Amazon) and see what humidity levels are. Or better yet, get an Internet smart thermostat.

Smart Thermostat with Relative Humidity

Get an Internet connected thermostat that monitors temperature and humidity

These let you to monitor indoor temperature and humidity levels while you are gone. These are affordable nowadays, and can give you tremendous peace of mind. A quick daily check on temperature and humidity gives you a read on the health of your home. It’s not a guarantee, as you still might have condensation problems, but at least you can be sure that the general climate inside your home is reasonable. It will also tell you that your heating system is working. If the temperature suddenly drops to 45 even though your thermostat is set to 55, you know there’s a problem and can call in help.

Have a wonderful winter. Hopefully you will avoid the main pitfalls that have hit too many other people. A few easy steps can greatly improve your odds of coming back to a healthy home!

How Should You Insulate Your Attic?

One of the hottest topics in energy efficiency and building science is “how should you insulate your attic?” Why? Simply put, the attic has more impact on your efficiency and comfort than any other single part of your home!

Let’s summarize why the attic is so important:

  1. The attic is the hottest part of the house in the summer and is cold in the winter
  2. Hot air rises up to the attic / cold falls drops into the living space
  3. Moisture rises and accumulates in the attic
  4. Central heating/AC systems and ductwork are often in the attic

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Why Doesn’t My Mini-split Heat Pump / Air Conditioner Work?

I recently had an interesting question – a reader asked what could cause a Fujitsu mini-split air conditioner to cause the air to become *more* humid. In fact, they noted that the air became highly moisture laden and the house was just yucky humid.

I really scratched my head on this one because, from a physics standpoint, under “normal” conditions, this is impossible with a mini-split. Why? Because a mini-split system has an air handler unit in the house with the only connection to the outside (and outdoor humidity) is through a small hole in the wall where the electrical and refrigerant lines run. And yet it happened.

The questioner noted that multiple units were involved and that various parts of the electronics had been changed, and yet the problem persisted. He noted that he’d heard of a number of other people with the same problem. I admit, I was baffled!

Then it came to me. In fact, I had worked with an associate, helping them to track down this exact problem. While I can’t state with 100% certainty that the problems were the same, the symptoms are the same. In addition, I realized that my own home’s systems exhibited the same issues, but I automatically made the adjustments to make the systems work properly!

Here’s what’s going on…

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Heating Systems 101 – Learning the Lingo

She Blinded Me With Science!

One of the toughest things about researching a new heating system is learning the tech talk. Your HVAC company will throw out all sorts of terminology assuming that you understand what they’re talking about. Some might even be happy that you *don’t* understand so they can confuse you and sound like experts. Well, no more!

This post covers the most common terms that you’re likely to run across. I’m sure I’ll miss some or confuse you, so please post questions if there’s anything you’d like clarified.

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