Slay Energy Vampires - Slay Energy Vampires Blog

I found a quick and easy way to calculate a home's energy efficiency. It allows for different fuel sources such as natural gas, propane, electricity, and even wood. It also takes into account your area's climate. I'll paste the steps below and then reveal how my own home fared.

Find out how many kilowatt hours of electricity, cubic feet of natural gas, gallons of propane and heating oil, and cords of wood you use in one year.
Convert to Btus. 1 kilowatt-hour of electricity equals 3,414 Btu, 1 cubic foot of natural gas equals 1,025 Btu, 1 gallon of propane equals 91,000 Btu, 1 gallon of heating oil equals 138,700 Btu, and 1 cord of wood equals 19 million Btu.
Divide the total number of Btus by the sum of the cooling- and heating-degree days (5,512 for Phoenix). Find your area's number here.
Divide the result by your home’s square footage.
If the result is under 10, you’re solidly energy efficient; 10-20, you’re doing fine; more than 20, you could stand to make some improvements.

My home used 12,139 kwh of electricity in 2008. I don't use natural gas, propane(grill use is negligible), or wood.

Multiply 12,139 kwh by 3,414 Btu/kwh = 41,442,546 Btu.

Divide 41,442,546 Btu by 5,512 heating and cooling degree days (hcd) = 7,518 Btu/hcd.

Divide 7,518 Btu/hcd by 1,750 sq ft = 4.3

I'm really happy with that number given the creators' assertion that anything under 10 is an efficient home. Like all approximations, this number isn't perfect, and it certainly doesn't tell the whole story - like how many people occupy this home, for instance. It does give an easy to remember point of comparison, though. I'd love to hear how other homes fare using this technique, so don't be shy if the math isn't too hard ;).

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