AFUE is an acronym for Annual Fuel Utilization Efficiency, which is a measure of how efficiently your furnace can utilize it's fuel. The more efficient your furnace, the more heat you will get per unit of fuel. AFUE - a thermal efficiency measure of space-heating furnaces and boilers, its not true 'thermal efficiency' because it is not a steady-state, peak measure of conversion efficiency, but instead it attempts to represent the actual, season-long, average efficiency of certain piece of equipment, including the operating transients.
For example, a 90% AFUE for a gas furnace means it outputs 90 BTUs of useful heating for every 100 BTUs of natural gas input (where the rest may be wasted heat in the exhaust). A higher AFUE means higher efficiency.
Some typical AFUE numbers |
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Fuel |
Furnace/boiler |
AFUE |
Heating oil |
Cast iron (pre-1970) |
60% |
Retention head burner |
70–78% |
|
Mid efficiency |
83–89% |
|
Electric heating |
Central or baseboard |
100% |
Geothermal heat pump |
see COP |
|
Air-source heat pump |
see HSPF |
|
Natural gas |
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Standard efficiency |
78–84% |
|
Condensing |
90–97% |