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AFUE

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

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

   

Standard efficiency

78–84%

Condensing

90–97%