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Annual Fuel Utilization Efficiency (AFUE)

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The AFUE is the most widely used measure of a boiler or furnace's heating efficiency. It measures the amount of heat actually delivered to your house compared to the amount of fuel that you must supply to the furnace. Thus, a furnace that has an 80% AFUE rating converts 80% of the fuel that you supply to heat -- the other 20% is lost out of the chimney.

Note that the AFUE refers only to the unit's fuel efficiency (i.e. natural gas, propane of heating oil), not its electricity usage.

The US Department of Energy determined that all furnaces sold in the US must have a minimum AFUE of 78%, beginning January 1, 1992. Mobile home furnaces are required to have a minimum AFUE of 75%.

Higher AFUE ratings will be required for furnaces and boilers sold after September 2015. These include:

  • non-weatherized gas furnaces: 80% AFUE
  • weatherized gas furnaces: 83% AFUE
  • mobile home gas furnaces: 80% AFUE
  • oil-fired furnaces: 82% AFUE
  • gas boilers: 84% AFUE
  • oil-fired boilers: 83% AFUE

The DOE's technical definition of AFUE is as follows:

The measure of seasonal or annual efficiency of a furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls.

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