AFUE (Annual Fuel Utilization Efficiency) Furnace 78% 90%
SEER (Seasonal Energy Efficiency Ratio, btu/watt-hr) Air Conditioner 10 13(2006) 13(energy star)
HSPF (Heating Seasonal Performance Factor, btu/watt-hour) Heat Pump 6.8 7.7(2006) 8.0(energy star)
1 watt-hr = 3.412 btu
For heat pump operating cost to be cheaper than furnace,
gas (therm)/electricity (kWh) price > 100 * AFUE(80%) / HSPF(7.7) = 10.39
Home Heating with Wood
Firewood for Home Heating
Purchasing and Preparing Your Fuel Supply
How much wood is in a cord of firewood? cord (4'x8'x4'), face cord (4'x8'x16"), stove/furnace cord (4'x8'x12")
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