A central furnace or boiler's efficiency is measured by annual fuel utilization efficiency (AFUE). The Federal Trade Commission (FTC) requires new furnaces or boilers to display their AFUE so consumers can compare heating efficiencies of various models. Specifically, AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90 percent means that 90 percent of the energy in the fuel becomes heat for the home and the other 10 percent escapes up the chimney and elsewhere. AFUE doesn't include the heat losses of the duct system or piping, which can be as much as 35 percent of the energy for output of the furnace when ducts are located in the attic.

 

Annual Estimated Savings for Every $100 of Fuel Costs by Increasing Your Heating Equipment Efficiency*