Technological advances in in gas furnace design have given homeowners more choices than ever, all of which are intended to increase indoor comfort while decreasing heating costs.

All gas furnaces consist of four main components: a burner, a heat excanger, a blower, and a vent pipe or flue.

These four components form the basis of three types of gas furnaces: a conventional warm-air furnace, an induced draft furnace, and a condensing furnace.

Conventional Warm Air Furnaces burn natural or propane gas to provide heat to the heat excanger. The air flows around the heat excanger and is then circulated throughout the house through the ducts. Other ducts return air that has cooled to the furnace to be reheated and recirculated. Additional air is drawn into the flue for venting purposes. This air mixes with the hot exhaust gases and exits through the chimney.

Induced Draft Furnaces are similar to conventional furnaces except for their venting method. Conventional furnaces draw air through an opening in the front of the furnace and at the flue to create a natural draft. Induced draft furnaces use a fan to draw the combustion products into the flue. This artificially created draft increases the efficiency of the furnace.

A Condensing Furnace is so named because it contains a second heat exchanger that condenses water vapor in the hot flue gases, thereby extracting additional heat for the home. Because the resulting flue gases are at a very low temperature, they can be vented directly outdoors through a plastic pipe that can run through a side wall. A drain disposes of the condensed water. Condensing furnaces are among the most efficient on the market.