High Efficiency Furnace

Furnaces heat air and distribute the warm air through a duct system.

The efficiency of a furnace is measured in Annual Fuel Utilization Efficiency (AFUE). An AFUE of 80% means that 80% of the fuel is converted to heat, while 20% is lost. High efficiency furnaces have AFUEs of 90% to 98.5%, plus sealed combustion and a second heat exchanger.

If your furnace or boiler is more than 20 years old, chances are that replacing it with a high-efficiency model may be a good investment. You may also consider a replacement if your system is an old coal burner that was switched over to oil or gas, or if it is an older model gas furnace without electronic ignition. If your furnace has a pilot light, this means that it was probably installed prior to 1992 and has an efficiency of about 65% efficient. By comparison, the least efficient systems today are 80%.


When replacing your furnace, you should look for one with the ENERGY STAR label. ENERGY STAR qualified furnaces have higher Annual Fuel Utilization Efficiency (AFUE) ratings and higher efficiency blower motors, which means that they are more efficient than conventional furnaces. In fact, according to ENERGY STAR, "if every gas furnace sold in the U.S. meets the new ENERGY STAR requirements, consumer energy cost savings would grow to about $171 million per year and annual greenhouse gas emissions would be reduced by the equivalent of those from about 177,000 cars".

ENERGY STAR labels furnaces differently in the Northern and Southern U.S. ENERGY STAR labeled furnaces in the Northern U.S. are up to 16% more efficient than the baseline (saves $94 per year), while Southern U.S. furnaces are up to 12% more efficient (saves $36 per year).

Installing or Repairing a Furnace

In some cases, it may be more cost effective to retrofit an existing furnace than to purchase a new one. The type of retrofit will depend on the furnace's fuel source (gas or oil). Examples of energy saving furnace retrofits may include vent dampers, a modulating aquastat (or outdoor reset), or time delay relay.

All furnaces should be installed or repaired by a qualified heating system professional.


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