How do furnaces work?
Gas – and oil-fired furnaces provide warm, even heat throughout your home by circulating heated air through ducts. The heat is created by burning the fuel (gas or oil) inside your furnace. (furnaces use outside air to help burn the fuel.) When the fuel burns, the hot gases that are created go through curved metal tubing called a heat exchanger and then out of your home through a metal or plastic vent pipe. At the same time, the air that circulates through your ducts passes over the outside of the heat exchanger and takes on the heat from the hot metal. The warm air is then circulated through your home. (By keeping combustion air and supply air separate, the heat exchanger allows the air in your home to be heated without contaminating it with the toxic by-products of combustion.) Some furnaces offer additional features that provide greater comfort (as well as additional energy savings). Two-speed furnaces can run on low speed up to 80% of the time, so they operate more quietly and run f
