How to Calculate the Size of a Furnace for a Home

Every home needs a heat source.

Furnace sizes are categorized by the number of BTUs the unit is capable of generating. BTU stands for British thermal unit, which is a measure of energy. By calculating the number of BTUs you will need to heat your home, you will avoid purchasing a heater that is too weak or too strong. A weak furnace will result in an improperly heated home, while one that is too large that is will cause the heater to operate less efficiently and raise your heating costs.

Instructions

1. Determine the square footage of your home. To do this, use the "square footage finder" at realestate.yahoo.com (see References for link). After you click on the finder, a new webpage will appear. Type your address into the text field at the top of the new page, and click "search." Your home's square footage will automatically be displayed on the screen.

2. Find the climate zone in which your home is located. To do this, look at the "climate zone map" at acdirect.com (see References for link). Each zone requires a different number of BTUs for a furnace.

3. Write down the climate zone BTU requirement associated with your home's climate zone. For example, if your home is located in the yellow climate zone, zone three, your climate factor would be 40 to 45 BTUs per square foot.

4. Multiply your home's square footage by its climate zone factor. For example, if your home is 1000 square feet and is in zone three, multiply 1000 by 40 giving you 40,000. This 40,000 represents the minimum number of BTUs that a furnace should be capable of outputting in order to heat your home.

Tips & Warnings

• A single BTU represents the amount of energy needed to raise 1 lb. of water one degree Fahrenheit.

References

• Alpine Home Air: Furnace Information
• Yahoo Real Estate: Square Footage Finder
• AC Direct: Climate Zone Map