Gas Furnace Basics

The efficiency of a furnace is rated using a percent of AFUE. A gas furnace uses natural gas

The furnace is the indoor unit that heats and circulates warm air through your home in the winter, and in the summer, it takes the cool air from the outdoor unit and works as a fan to circulate it throughout your home. The indoor and outdoor units are designed to work together.  Furnace heating ability is gauged with an Annual Fuel Utilization Efficiency (AFUE) percentage. A higher AFUE percentage indicates a more efficient furnace.

The basic components of a gas furnace system:

  • A Burner, through which gas is delivered and burned. 
  • A Heat Exchanger, where the heat produced from the burning gas is transferred to the air distribution system. 
  • Ductwork, to transfer the heated air throughout the home. 
  • A Flue or Vent Pipe, to exhaust byproducts of combustion (such as water vapor and carbon dioxide) to the outside. 


Furnace’s Air Handling System:

Single Stage Furnaces:  Modern single-stage furnaces offer new features not found on older furnaces. Features include an inducer to draw the most efficient quantity of air into the furnace, an electronic ignition system to replace the old wasteful pilot light, and a direct-drive blower that sends warmth to all the rooms in your home. These features can help make your home more comfortable and reduce heating fuel bills.

Two-Stage Furnace: Two-stage furnaces operate at low capacity during most of the operating cycle to reduce heating expenses while maintaining your level of comfort. On bitterly cold days, the second stage is available to produce extra heat.

Variable-Speed Furnace: These furnaces circulate more air throughout the home for longer periods of time, reducing air stratification room-to-room and floor-to-floor. This feature improves air quality by increasing air filtration. Variable-speed furnaces also offer significant operating cost savings and quiet operation.