It’s a techno-acronym for a measurement of furnace efficiency that is monitored by the U.S. Department of Energy (DOE), and stands for Annual Furnace Utilization Efficiency. The rating is a percentage and, for example, a furnace with an 82% AFUE converts 82% of the fuel used into heat, with the other 18% wasted--typically up the flue and into the atmosphere.

   The DOE mandated in 1992 that all furnaces sold in the U.S. must have a minimum AFUE of 78%, with mobile homes allowed a slightly reduced AFUE of 75%. Mid-range efficiency furnaces have an AFUE of 78 to 82%, and high efficiency systems are AFUE-rated at 88 to 97%. A high-efficiency gas furnace is easy to spot, because so much heat is extracted and the exhaust gases have been cooled-down enough that a white-plastic PVC pipe is used as a flue.

   It’s important to note that the AFUE is a measure of fuel efficiency, not fuel usage. Also, the DOE’s calculation takes into account the on/off cycles and changes in load over the course of a heating season. 

    Also, see our blog post Is the energy efficiency of the furnace part of the SEER rating of a central air conditioning system? 

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.