Conventional Furnaces

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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.

How a Gas Furnace Works

How a Gas Furnace Works

In a gas furnace, cold air is pulled into the return register and is heated by the heat exchanger; a series of gas burners within a combustion chamber. The hot air is pushed out and distributed through the house. Exhaust from the gas burners exits the building through an exhaust vent.

Is this a forced air or gravity heating system?

Answer: Forced air because both warm and cold air travel through the ducts.

 

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.

How an Electric Furnace Works

How an Electric Furnace Works

A motor-driven fan pulls air into the return register. The air passes through a filter and moves past electric heating elements. The now warm air is pushed out the system and distributed throughout the house.

Is this a forced air or gravity heating system?

Answer: Forced air because both warm and cold air travel through the ducts.