What Are the Different Parts of a Gas Furnace?

There are four types of furnaces: electric, dual fuel, gas, and oil; however, all of the most efficient types of furnaces recognized by EnergyStar® are gas. Today’s gas furnaces can achieve as much as 98% fuel efficiency using fresh air from the outside.

How a gas furnace works depends on the type; it can be a single-stage, two-stage, or modulating furnace. The basic parts of a gas furnace are the burner, heat exchanger, ductwork, and ventilation pipes or flue. But there are other mechanisms and parts that combine to deliver clean, warm air to the rooms in your home. Here are some of those furnace components and what they do:

• Return ducts – Retrieves cooled air from home and returns it back to the furnace to be reheated.
• Air filter – The air filter catches dust, debris and particles in the air before the air enters the blower motor.
• Blower motor – Pushes the air past the heat exchanger into the supply plenum for distribution throughout your home.
• Supply plenum – This is a duct that is attached to the furnace; it distributes heated air throughout your home.
• Thermostat – This measures the temperature inside your house and “tells” the ignitor when to turn on.
• Hot surface ignitor – After the thermostat has signaled it to turn on, an electrical current is sent to the ignitor, which then lights the burner.
• Burners – Fuel is sent to the burners, which are ignited by the hot surface ignitor to produce a consistent, controllable flame that sends heat to the heat exchanger.
• Heat exchanger – This is the place where combustion gasses enter. The heat from the gasses is absorbed into the walls, and the combustion gasses are cooled and vented into a pipe.
• Flue – The unwanted exhaust – which contains carbon monoxide – is sent to the flue and channeled outside.