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 located inside a combustion chamber. There, the gas is mixed with air, then ignited by a pilot light, a spark, or a similar device controlled by a thermostat. The flame heats up a metal box—the heat exchanger—where room air is heated as it flows through. Exhaust gases 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.
Instructions: Press the play button to see how a gas furnace works, and then answer the question that follows.
An electric furnace uses heating elements rather than burners to heat in the heat exchanger.
Instructions: Press the “play” button to see how an electrical furnace works, and then answer the question that follows.