How do I know if my boiler (or furnace) is the correct size for my house?

If you are thinking about purchasing a new boiler (or any other heating appliance) in the near future, make sure that you get one that is the optimal size for your house. Correctly sized boilers operate more efficiently and are able to keep your house at a comfortable temperature. A boiler that is too small will not be able to produce enough heat in the winter months, and a boiler that is too large will cycle on and off, wasting fuel, just like a car driving in stop-and-go traffic. Here are 3 ways to know if your current boiler is the correct size:

1) The rule-of-thumb: On the coldest day of the year, your boiler should run pretty much non-stop to keep the set temperature. Think of it as a car driving on the highway, getting a high miles-per-gallon since it doesn’t have to start and stop. If it does run non-stop, but your house does not stay warm, then the boiler is undersized. On the other hand, if you find your boiler cycling on and off during January’s coldest week, then you should consider getting a smaller boiler.

2) The calculations method: To determine what size of a heating appliance you will need, in addition to finding out information about what other energy upgrades you can make to your house, consider signing up for an energy rating. An energy rater will look at your entire house, measuring the air leakage rate with depressurization from doors and windows, checking insulation levels, assessing your heating system and checking for drafts. They will input this information into AKWarm, software maintained by the Alaska Housing Finance Corporation that calculates energy ratings. In a few weeks, you will receive the rating in the mail. It includes ways to improve the rating and other information on your house, such as the heating needs. An energy rating typically costs between $425-$550, but this will be rebated if you participate in the Home Energy Rebate Program (though you will likely face a waitlist for the rating). Visit the Alaska Housing Finance Corporation website for information on the rebate program and signing up for a rating:

3) Do-it-yourself: The rating software AKWarm is available for free online. If you are computer-savvy and have a few hours to gather information on your house, you can use AKWarm to calculate your own unofficial energy rating. The software is available for download here: