Upgrading to a high efficiency furnace is an effective way to save money on home heating.
Most U.S. homes are heated with either furnaces or boilers. Furnaces heat air and distribute the heated air through the house using ducts.
A central furnace’s efficiency is measured by annual fuel utilization efficiency (AFUE). The Federal Trade Commission requires new furnaces to display their AFUE so consumers can compare heating efficiencies of various models. AFUE is a measure of how efficient the appliance is in converting the energy in its fuel to heat over the course of a typical year.
Specifically, AFUE is the ratio of annual heat output of the furnace compared to the total annual fossil fuel energy consumed by a furnace. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% 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% of the energy for output of the furnace when ducts are located in the attic, garage, or other partially conditioned or unconditioned space.
An all-electric furnace has no flue loss through a chimney. The AFUE rating for an all-electric furnace is between 95% and 100%. The lower values are for units installed outdoors because they have greater jacket heat loss. However, despite their high efficiency, the higher cost of electricity in most parts of the country makes all-electric furnaces an uneconomic choice. If you are interested in electric heating, consider installing a heat pump system.
You can identify and compare a system’s efficiency by not only its AFUE but also by its equipment features.
Old, low-efficiency heating systems:
- Natural draft that creates a flow of combustion gases
- Continuous pilot light
- Heavy heat exchanger
- 56% to 70% AFUE.
Mid-efficiency heating systems:
- Exhaust fan controls the flow of combustion air and combustion gases more precisely
- Electronic ignition (no pilot light)
- Compact size and lighter weight to reduce cycling losses
- Small-diameter flue pipe
- 80% to 83% AFUE.
High-efficiency heating systems:
- Condensing flue gases in a second heat exchanger for extra efficiency
- Sealed combustion
- 90% to 98.5% AFUE.