Annual Fuel Utilization Efficiency.

AFUE is the abbreviation for the Annual Fuel Utilization Efficiency ratio. AFUE is used to rate furnace efficiencies by dividing the ratio of heat output by heat input. This measurement describes and determines how efficiently the furnace consumes fuel, gas, or oil in order to produce heat. As the AFUE rate increases, the efficiency of your furnace also increases—thus lowering your fuel costs. Furnaces manufactured in the United States are required to have at least an 80% AFUE.