If you're in the market for a new gas furnace, do you know the differences between a conventional, induced draft, and condensing furnace?

If you don't, you should because your choice of furnace design will have an effect on its efficiency, and that, in turn, will have an effect on your annual heating costs.

Heating experts at the Trane Home Comfort Institute explain that all gas furnaces consist of four main components: burners where the gas is delivered and burned; heat exchangers that transfer the heat from the burners to the home's air distribution system; a blower that moves the heated air through the ducts and into the home; and a flue that exhausts the gaseous byproducts of combustion to the outdoors.

The four components form the basis of the three most common types of gas furnaces: conventional, induced draft, and condensing.

Conventional furnaces burn natural or propane gas to provide heat to the heat exchanger. Indoor air flows around the heat exchanger to be heated and then circulated throughout the house through the ducts. 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 through the heat exchangers and then into the flue. This artificially created draft increases the efficiency of the furnace.

Condensing furnaces contain a second heat exchanger that collects heat from the hot flue gases, yielding 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. Condensing furnaces are the most efficient on the market.

If you still have questions about gas furnaces, the Trane Home Comfort Institute recommends that you contact your local heating contractor. He can answer them for you and recommend the best heating system for your home.