What AFUE Means to Household Comfort and Energy Efficiency

Having a furnace working efficiently is what keeps your energy bills down. In order to measure heating efficiency and enable consumers to compare between models, furnaces are rated by their annual fuel utilization efficiency (AFUE). Shown as a percentage, AFUE measures how well the furnace can convert fuel into heat for your home. An AFUE of 80 percent means that 80 percent of the fuel will be used for heating your home, and 20 percent either won’t be converted to energy or will be lost through the chimney.

Aside from the AFUE rating, there are other characteristics of a system’s efficiency (or lack thereof). Some things to look for include:

  • Low-efficiency (older) system: heavy heat exchanger, pilot light continuously lit, uses natural draft to supply combustible gases, and a typical efficiency rating between 56 and 70 percent.
  • Mid-level efficiency system: compact and lighter to reduce losses through cycling, electronic ignition in lieu of pilot light, an exhaust fan to control combustible gas supply and exhaust, and a typical rating between 80 and 83 percent.
  • High-efficiency system: condenses flue gases in a secondary heat exchanger to provide added efficiency, completely sealed combustion, and a rating between 90 and 98.5 percent.

Upgrading an older, low-efficiency furnace to a new model could provide significant energy savings to you. For instance, going from an ancient furnace with 55 percent efficiency to a unit with 90 percent AFUE will cut your energy bill by over 38 percent. Higher AFUE furnaces do cost more, and the payback period of a new furnace also depends on climate. In cold-winter areas, the monthly energy savings from a high-efficiency furnace will be greater than in an area with mild winters.

It’s important to note that even a very high AFUE furnace will not work well if you do not have a properly insulated and sealed house or ductwork that leaks. To get the most out of whatever rating your furnace has, make sure to consult a contractor with NATE-certified technicians to determine whether additional work to your insulation, air sealing or ductwork could improve the level of comfort and energy efficiency in your home.

For more information related to furnace efficiency and other issues dealing with home comfort, contact the experts at Roscoe Brown, Inc. We have been proudly serving the Nashville and Middle Tennessee area for over 70 years.

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