What to look for in a new hot water based (boiler) heating system


I got a great question from a reader asking about replacing a boiler and water heater system. After writing a reply, I realized the information might be useful to others, so here goes!

If you’ve got an old boiler that you’re thinking about replacing, you might find all the terminology and technology a bit intimidating. Fortunately, these days, there are a quite a few safe, high efficiency, hot-water generating systems that can provide plenty of hot water for baths and showers as well as heating your home.

I’ve been using this type of system in my home for years, both oil and gas (actually propane, but for this discussion, they’re the same). They can be excellent and cost effective IF configured and controlled correctly.

Let me get something out of the way right away – I would *not* recommend an oil burning system. Even though oil has come way down in price, it’s simply not a great fuel for home heating systems for a number of reasons

  • Oil is dirty and smelly. A couple of drops of heating oil stinks. When it burns, the sulfur stinks. If it spills, or your tank leaks, you can have a huge bill for environmental cleanup. Avoid it at all costs. I was finally able to get rid of my oil based system and I still need to pay someone to take the tanks away. Blah!
  • Oil burns dirty. In the United States, most home heating oil has a relatively high sulfur content. There’s two problems with this. Did I mention it smells? Burning sulfur smells like like rotten eggs. But most people don’t go around smelling their boiler’s exhaust. The worse problem is that sulfur plus water gives you sulfuric acid. This is nasty stuff! I had a high-efficiency European oil-burning boiler that rusted through it’s stainless steel heat exchanger in a few years! European heating oil is ultra-low sulfur, so they don’t have this problem as much and they don’t design for low-grade American heating oil.
  • Seasonal cleaning – you’re going to spend a couple hundred dollars every year for a contractor to come in and clean out all the crap from your oil burner. If you don’t, it will run less and less efficiently or fail to work at all, then you’ll spend even more for an emergency service call.
  • Because of the sulfuric acid problem, there are very few truly high efficiency oil based boilers. I’ll get hate mail from the manufacturers. But it’s true. All the contractors will tell you don’t need one of these new-fangled high-efficiency boilers. They’ll tell you to get a good ‘ol cast iron boiler. They’ve been rock solid for 100 years and can last decades! But you know what? I don’t want 100 year old, dirty, inefficient technology when I can buy a clean burning gas or propane system that requires minimal maintenance, runs super-efficiently, is so light that it can be hung on the wall, and burns so quietly that you won’t know it’s on.

Now that I’ve gotten that out of the way, let’s get on to more fun stuff.

First, in this day, I wouldn’t consider anything but a condensing boiler. Combustion efficiency is 92+ % and they’re far safer because they are sealed direct exhaust systems – they take fresh air from the outside and directly pipe the exhaust out, usually through a hole in the side wall of your utility room.

With less efficient systems, you often have natural venting, which uses convection (hot air rises) to get the exhaust fumes out of the house. Plus, they take air from the living space. Put this in your basement with the dryer and turn on a bathroom fan and you can literally suck the exhaust fumes back into the house. This type of system has no place in a modern home.

Next, a good (gas) boiler and control system modulates the combustion so that it burns less when the demand is low but can ramp up on a cold day or if you’re filling a tub while heating the house. This makes it even more efficient.

Another good feature is an outdoor temperature sensor that allows the boiler to change the heating water temperature based on your actual needs. This is called “outdoor reset.” Cold weather? It cranks up the temperature so the radiators get hotter. Better comfort and more efficient operation.

A key feature is the ability to flush out the remaining heat in the boiler after the call for the heat is satisfied (i.e. the thermostat turns off). This way, you waste less heat keeping the boiler hot. Instead, the boiler sends the heat to the water heater or the radiators.

Finally, and this is a big one, the boiler can operate in a “cold start” mode. In old, and even new boilers, the boiler stays hot year round! This can reduce actual efficiency down to 40% or worse because so much energy is wasted keeping it hot. With a cold start system, it only runs when there’s a need for heat. Before you (contractors) yell at me about this 40% figure, I measured it over several years and have analyzed other, properly functioning systems. I know this as fact. During the summer, most of your fuel is burned just to keep the boiler hot. A tiny fraction goes to actually heating your water. 40% is generous. In a small household, efficiency can be 25%, with 75% of your heating costs wasted.

Everybody asks for brand recommendations but most reviewers are squeamish about naming names. I’m not. After a lot of research and discussion with heating professionals, I purchased a Triangle Tube boiler. It has all the bells-and-whistles I mentioned and is very affordable. But all the main manufacturers have high quality gas/propane condensing boilers these days. Just find one that your contractor is familiar with so they’ll know how to install and fix it.

Natural gas or Propane?

If you have the option, get natural gas. It’s much less expensive than propane and, since it comes from a utility company, you don’t need a storage tank. Many places don’t have public gas so you have to get propane (like where I live). Then you’ll have to factor in a few thousand dollars for a big storage tank and you’ll pay a lot more for the fuel.

Even if you have to pay a few thousand dollars to run a line from the road to get natural gas, it’s worth it. It will pay for itself quickly compared to propane. But if propane is your only choice, go for it.

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5 thoughts on “What to look for in a new hot water based (boiler) heating system

  1. Hi Ted –

    I just installed a Triangle Tube Prestige Solo boiler as well. Love it so far. A few things I’d add:

    Make sure you’re installing the proper-sized boiler for your home’s heating needs. Be absolutely sure that your installer does a proper heat loss calculation for your house (sometimes known as a “Manual J”) – or perhaps better, have a 3rd party energy expert do it. It’s critical to get a right-sized boiler if you want it to run efficiently, and it’s all too common to install a boiler which is bigger than the home needs. This means that it can’t modulate down as far as it should, runs for shorter periods of time, and will be less efficient and less comfortable.

    You can take your own swag at a heat loss by using Taco’s “FloPro” software, it’s a fairly easy to use Windows application. It’ll at least get you in the ballpark, and see if your installer is blowing smoke when they recommend the largest boiler on the market. 😉

    After it’s installed, make sure it’s set up right, especially in terms of the outdoor reset curve. Sadly many installers leave it at factory defaults, which probably won’t be optimal for your home. I took the time to measure my radiator sizes, add up their heating capacity at certain water temps, and adjust the reset curve so that the boiler is putting just the right amount of heat into the home for a given outdoor temp.

    The Triangle Tube boilers have a Modbus interface which allows you to query their state, and this makes realtime monitoring possible . Check out http://sandeen.net/wordpress/energy/residential-boiler-monitoring-via-modbus/ if you’re interested in that, it helped me see what my boiler was doing, and tune it as well as I could.

      • This is a great post and I think between you and Sandeen you covered the topic very well. I would like to see this expanded with more info on the water heater portion of the system. Ted mentioned running a boiler in the summer and, of course, the only reason for that could be to make hot water. Cold start is absolutely necessary but I think also the addition of a heat pump water heater (why do they call them hybrids, they are 100% electric?) with some additional controls. I am thinking a thermostat and humidistat to control heat pump. This system would use the heat pump when the basement temp is high and humid (think summer) and the propane boiler as the back up. Or you could just use the heat pump and rely on the electric elements for back up and forget the boiler and extra controls. I am not an engineer like Ted so I am unable to compare the cost of running a propane boiler all summer versus a heat pump with electric elements for summer use and temp and humidity controls.

        This is not my idea by the way, I got it from a post on LinkedIn and I can expand on that concept if it interests you.

      • Thanks for the input Kent. Those are great ideas. I’ve been looking for topics and appreciate your feedback. This sounds like it could be a very useful series of articles on a topic that almost everybody could benefit from.

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