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Encyclopedia > Annual fuel utilization efficiency

The annual fuel utilization efficiency (AFUE; pronounced 'A'-'Few') is a thermal efficiency measure of combustion equipment like furnaces, boilers, and water heaters. The AFUE differs from the true 'thermal efficiency' in that it is not a steady-state, peak measure of conversion efficiency, but instead attempts to represent the actual, season-long, average efficiency of that piece of equipment, including the operating transients.[1] The thermal efficiency () is a dimensionless performance measure of a thermal device such as an internal combustion engine, a boiler, or a furnace, for example. ... A furnace is a device for heating air or any other fluid. ... A boiler is a closed vessel in which water or other fluid is heated under pressure. ... A trio of propane hot water heaters. ...

The method for determining the AFUE for residential furnaces is the subject of ASHRAE Standard 103. A furnace with a thermal efficiency (ηth) of 80% may yield an AFUE of only 64% or so, for example, under the Standard's test conditions. When estimating annual or seasonal energy used by combustion devices, the AFUE is the better efficiency measure to use in the calculations.[2] But for an instantaneous fuel consumption rate, the thermal efficiency may be better.

See also

The coefficient of performance, or COP (sometimes CP), of a heat pump is the ratio of the output heat to the supplied work or where Q is the useful heat supplied by the condenser and W is the work consumed by the compressor. ... The efficiency of air conditioners are often (but not always) rated by the Seasonal Energy Efficiency Ratio (SEER). ... Seasonal Energy Efficiency Ratio (SEER) is a measurement of efficiency for cooling devices such as heat pumps and air conditioners. ... The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) is an international voluntary organization for people involved in heating, ventilation, air conditioning, or refrigeration (HVAC&R). ...


  1. ^ Systems and Equipment volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, USA, 2004
  2. ^ Heating and Cooling of Buildings, Kreider and Rabl, McGraw-Hill, New York, 1994



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