Forced-air heating

A forced-air heating system draws room air through ductwork and a filter into a furnace, where the air is heated. The warmed air is then blown back to rooms through ductwork. With older "gravity" furnaces, the heated air is delivered by natural convection, not by a blower.

Most furnaces are gas-fired, but other fuels include oil, coal, wood and electricity. With a conventional furnace, natural gas is piped to a burner that's located inside a combustion chamber. There, the gas is mixed with air, then ignited by a pilot light, a spark or a similar device that is controlled by a thermostat. The flame heats up a metal box-the heat exchanger- where room air is heated as it flows through. Exhaust gasses given off by burners vent outside through a flue that goes up through the roof or, with newer high-efficiency models, out through a wall. An electric forced-air furnace uses heating elements rather than burners to heat in the heat exchanger.

MORE ABOUT:
/ Upflow furnaces / / Forced air furnace systems / / Radiant hydronic heating / / Hydronic radiators /
/ Air conditioning / / Heat pumps / / Thermostats / / Air cleaners /

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