How to Calculate BTUs to Heat Your Home

Written by elizabeth knoll
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How to Calculate BTUs to Heat Your Home
Knowing room sizes will help you choose heaters with the correct capacity. (Jupiterimages/Pixland/Getty Images)

Installing a furnace that outputs the correct number of BTUs (British Thermal Units) is critical for both home comfort and maintaining a low energy bill. Install a furnace that is too small, and you will not be able to maintain comfort levels. Install a furnace that is too large, and you will spend an excessive amount of money on your energy bill. Sizing is calculated by using a certain BTU number per square foot of floor space in your home. This number varies depending on your location and the insulation quality of your home.

Skill level:

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Things you need

  • Tape measure
  • Calculator

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  1. 1

    Start in one room of your home and measure its length and width. Multiply these two figures together to find the square footage of the room.

  2. 2

    Calculate the square footage of each additional room in your home using the method described in Step 1. Add the square footage of each room together to end up with the total square footage of your home.

  3. 3

    Allow between 30 BTUs per square foot and 60 BTUs per square foot, depending on the region where you live (see the References section).

  4. 4

    Multiply your home's square footage by the BTU allowance from Step 3. For example, if your square footage is 2,000 and you are using 40 BTUs per square foot, you will need 80,000 output BTUs from your furnace.

Tips and warnings

  • If your home is newer and well-insulated, use the lower number in the range of BTU for your zone. If your home is not well-insulated, use the higher number in the range.

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