How a Furnace Works A furnace works by drawing air inside a heat exchanger, where it is warmed with a flame of natural gas, propane or fuel oil, or with heated electric coils. Indoor air is circulated continuously through the system, so a furnace filter is used to contain dust, pollen and other airborne particles. An older home might have a boiler, fueled by natural gas, liquid propane or fuel oil. A boiler works by heating water and circulating is through pipes to radiators, where it warms the surrounding air. Another home heating option is an electric heat pump.
Indoor air is warmed in the heat exchanger and circulated throughout the home.
During the summer, the process is reversed to cool and dehumidify the home. Geothermal systems are usually installed in newly-built homes, but can also be used in existing home. One advantage of a heat pump is that it provides both heating and cooling capabilities in one unit. Heat pumps also use filters to reduce airborne particles and keep the unit clean. Electric Resistance Heating Electric resistance heating, usually found in the form of baseboard heaters, was popular during the 1940s and 1950s, and is often used in multi-family dwelling like apartment houses.