Low Efficiency Furnace

An 80% gas furnace is a type of heating system that is designed to burn natural gas or propane to heat the home. The “80%” in the name refers to the furnace’s Annual Fuel Utilization Efficiency (AFUE) rating, which indicates how much of the fuel consumed is actually converted into usable heat. An 80% AFUE rating means that the furnace converts 80% of the fuel it consumes into heat, while the remaining 20% is lost through the exhaust.


Here are some key features of an 80% gas furnace:

  1. Single-Stage Burner: Most 80% gas furnaces have a single-stage burner, which means that the burner is either on or off. When the thermostat signals that the temperature has dropped below the desired level, the burner turns on and heats the air.
  2. Standard Venting: 80% gas furnaces typically use a standard metal flue pipe to vent the combustion gasses out of the home. These gasses contain water vapor and other pollutants, so proper venting is essential to prevent indoor air quality problems.
  3. Pilot Light: Most 80% gas furnaces use a standing pilot light to ignite the burner. This requires a constant flow of gas to keep the pilot light burning, which can contribute to energy waste.
  4. Traditional Thermostats: 80% gas furnaces are typically compatible with traditional thermostats that allow homeowners to manually adjust the temperature.


While 80% gas furnaces are less efficient than high efficiency furnaces, they are still a popular choice for many homeowners due to their relatively low upfront cost. They are also widely available and can be used in a variety of heating applications, including forced air and hydronic (water-based) systems. Regular maintenance, including cleaning and inspection of the furnace and flue, is essential to ensure proper function and safety.

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