The heating and cooling industry uses a number of ratings systems to determine the efficiency of its products, and understanding the numbers that they toss around can be crucial for a homeowner hoping to upgrade or purchase new equipment.

One of the most commonly quoted numbers when looking at heating equipment is the AFUE, or Annual Fuel Utilization Efficiency. This is the standard that measures how efficiently gas- and oil-fired furnaces use energy. The number is stated as a percentage representing how much fuel is actually being used to heat the home and how much is wasted as the furnace operates. The AFUE represents the unit’s average efficiency over a season of use, rather than a steady state.

The Federal Trade Commission requires new furnaces and boilers to display their AFUE to make comparing efficiency among different brands and models easier. The higher the AFUE number, the less fuel the furnace wastes. For example, if a furnace has an AFUE rating of 90 percent, the furnace outputs 90 BTUs of heating energy for every 100 BTUs of energy the furnace consumes. It loses 10 percent of the energy in its operation, usually as heat out of the chimney. Heating systems may lose additional heat through duct systems or flues, particularly when located in attics or garages. However, the AFUE number does not take these heat losses into account; the number is based on the efficiency of the unit itself.

AFUE ratings vary both by type of fuel used in a unit and by grade of equipment. Currently, the heating systems with the greatest efficiency are all-electric furnaces or boilers, which have AFUE ratings between 95 and 100 percent. For new central-heating equipment of the gas or oil variety, the table below shows the average efficiency levels available for the top four types of heating systems.

AFUE Efficiencies

Type of Fuel Average Range of Efficiency
Gas Furnace 80% - 98%
Oil Furnace 80% - 87%
Gas Boiler 80% - 98%
Oil Boiler 82% - 95%

In modern heating systems, both mid-level and high-efficiency equipment have many features that help support efficiency and improve the unit’s overall AFUE.

Mid-level heating systems:

  • 80 to 83 percent AFUE
  • Electronic ignition (no pilot light)
  • Compact size and lighter weight to reduce cycling losses
  • Small-diameter flue pipe

High-efficiency heating systems:

  • 90 to 98.5 percent AFUE
  • Flue gas condensing in a second heat exchanger for extra efficiency
  • Sealed combustion

For homeowners, being able to compare heating systems with a standard number like AFUE can make it much easier to choose a path toward a comfortable, energy-smart, and money-saving home.

Click Here to View Your Local Best Pick® Air Conditioning & Heating Contractors

Sources: American Council for an Energy-Efficient Economy; Carrier; ENERGY STAR; US Department of Energy.

For more information on our sources, please contact us directly.