How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What does the AFUE rating of a furnace mean?
Monday, October 8, 2018
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.
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To learn more about heating and air conditioning systems, see these other blog posts:
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