Boiler vs. Furnace

Do you know if your house has a boiler or a furnace? Don’t be too concerned if you don’t, we find most people tend to use the word “furnace” to describe the mechanical unit that heats their home and they really have no idea whether it’s a furnace or a boiler. But wouldn’t it be nice to know the difference? And then you could use the right term the next time you’re talking to your trusty heating contractor.


A boiler heating system uses fire to heat water which then distributes heat to the home via a series of pipes leading to radiators, either baseboard or the older cast iron versions.

A furnace heating system heats air which is distributed through the home via duct work, powered by a blower motor.

If you see vent grates in your floor, baseboard or ceiling, you have a furnace. If you have baseboard or cast iron radiators, you have a boiler.

Both boilers and furnaces can be powered by oil or gas.

The more you know…

*A special thanks to reader Brooks for the picture of an ornate heating grate in his home.

14 thoughts on “Boiler vs. Furnace”

  1. Also, do you find that most boilers are of the Hot Water variety? When we rented in Glastonbury, our boiler was steam and it was oh so toasty warm.. 🙂

  2. Brooks, most of the radiator-type heating systems we come across are hot water, not steam. I can probably count on one hand the number of houses I’ve sold with steam radiators. Not sure why they’re less common, but around here they just seem to be.

  3. Steam is also a lot less efficient, unfortunately. Boilers can get into the 90s for efficiency ratings, steam usually tops out at 83% efficiency even on the latest units. Still better than a lot of the older models, but not anywhere near what most people are looking for these days!

  4. I always love reading your blog however I have to correct you on this boiler/furnace position. Grilles/grates do not necessarily mean that you have a furnace. A boiler does make hot water as you state, but this hot water could then either feed radiators or a separate air handler which would convert that hot water to hot air via a radiator type process. Many times, a central boiler will be installed in a larger house which would then serve a number of purposes; as your domestic hot water source (hot water for your shower etc.) and feed a number of different air handlers spread throughout the house. This is a very efficient way to provide heat and hot water throughout a larger house, hot water is much more efficient way to carry heat energy than hot air. In my house, I have one very efficient boiler located in my basement, which serves as my domestic hot water source, feeds an air handler also in the basement which serves the hot air ductwork for the first floor, and an air handler located in the attic which feeds the ductwork for the third floor. Figuring out whether you have a boiler or furnace can only be determined by looking at the actual unit, not just by looking at the radiators/ductwork etc. The inverse can be true though, if you have radiators then you must have a boiler, however, if you have ductwork it doesn’t necessarily mean that you have a furnace.

  5. Christian, thanks for the clarification. Yes, technically you should look at the actual system to determine if it’s a furnace or boiler.

    The system in your house that you’re referring to is a hydro air system, for readers who are not familiar with this type of heat. Honestly, I can count on one hand the number of times I’ve seen a hydro air system out of the thousands of houses I’ve seen, whether older or even new construction. For older houses very few people ever change what was originally put into a house for heating, they just change the unit, whether it’s a boiler or furnace. And for the new builds I’ve seen, it seems everyone uses a furnace. My guess is that it’s a cheaper system than going with hydro air because you only have one piece of mechanical equipment to buy, rather than both a boiler and one or more air handlers.

  6. I think the hydro air setup might be more common in commercial construction, although I am certainly no expert along the lines of Mr. Winkley…

    At my previous employer in State College, PA they built a new building that used geothermal technology. There was an actual Heath Exchanger unit in the basement (as opposed to using the ground for heat exchange purposes), built by ITT Industries, which would then send hot or cool water out into the building loop to individual heat exchange units. These units would either draw heat off or put heat into the water, and a blower would push the warm or cool air from ceiling vents.

  7. And I’ve seen a total of 1 geothermal heating system in a house. Ever. Nobody around here does this stuff. It’s the land of steady habits which I find translates to “we don’t like anything new!”

  8. No, all of New England is the same. Technology, and just about everything, starts in the West and eventually makes its way East.

  9. Sorry to swoop in with a late response, but I’m surprised that most new homes are being built with forced air heat. I realize it is economical as one delivery system can handle air conditioning and heat, but I strongly prefer hot water heating (radiators, baseboard) for winter heating over forced air heat (which even in well-designed systems can feel drafty and uneven in addition to being noisy). The total efficiency of the system is also, I believe, higher than in air based systems.

    My favorite system, which I’d use in a new build or if I was installing a new system in my home, would be cast iron baseboard. Quiet, even distribution, slow to heat up and cool down, doesn’t take up much floor space.

    Sorry to go all house geeky on you.

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