Furnace Facts: Know the Parts of Your Furnace

You tap your thermostat to lower or raise the temperature, and the corresponding air flows from the vents. But what's really happening behind these visible parts of your HVAC system?

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What Are the Different Parts of Your Furnace?

Not all furnaces are the same, but to create heat for your home, gas and electric furnaces do tend to rely on the same parts. Here's a look at some of the most important parts of your furnace.

Heat Exchanger — Gas and Electric Furnaces

The heat exchanger is a group of metal coils wrapped around a central component. In a gas furnace, the gas burns inside the tubes to generate heat. The resulting hot air, once separated from carbon monoxide or other harmful fumes, is transferred into your home via ductwork. The heat exchanger in an electric furnace operates differently, relying on electric heating coils, but the end result is the same.

Blower Motor (and Capacitor) — Gas and Electric Furnaces

The blower motor is the component that pushes the hot air through ducts and into spaces where you want a change in temperature. The capacitor helps control the motor, causing it to turn on at the desired time and helping control the speed at which it runs.

Thermostat — Gas and Electric Furnaces

The thermostat is your furnace's control station. You can use it to turn the unit on and off, switch modes or change the desired temperature.

Ductwork — Gas and Electric Furnaces

Ductwork is a separate component from your furnace, but without it, your furnace would be fairly useless. This is the tubing throughout your home that allows warm air generated by the furnace to travel to different rooms.

Return Air Filters — Gas and Electric Furnaces

Again, this component is not specifically part of the furnace. It goes into the return air vent to help remove debris and dust from air that passes through the air filter and flows through your unit and into your home. It's critical to ensure the filter is changed or cleaned regularly to protect the quality of air in your home and the components in the furnace and other parts of your HVAC system.

Contactor — Electric Furnaces

The contactor works to open or close the switch that allows electricity to power up furnace heating coils. It does this based on how you set your thermostat.

Sequencer — Electric Furnaces

This is the component that controls whether heating elements are turned on or off. All the heating coils or elements in your electric furnace may not operate at once, and the sequencers ensure the elements take turns to avoid drawing too much power.

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Transformer — Electric Furnaces

The transformer allows power to move into the furnace, transferring electricity from circuit to circuit as needed.

Gas Valves — Gas Furnaces

These valves reduce the gas pressure coming from the utility company, county or another source to a pressure that works with your furnace. Without a working valve, the gas might reach the unit at too high a pressure and cause damage.

Pilot Light, Igniter or Thermocouple — Gas Furnaces

Gas furnaces depend on a flame to ignite incoming gas, creating the burn that drives heat. The pilot light offers this flame. Depending on the age of your furnace, the pilot light might burn all the time so it's ready to ignite incoming gas the minute you turn on the furnace and cause gas to start flowing.

Newer furnaces may have an igniter that causes the pilot light to come on only when the gas supply is switched on. To support safety in older gas furnaces where pilot lights burn constantly, a part called a thermocouple senses whether the pilot light is on. If it's not, the thermocouple doesn't allow gas to flow through, as it won't be burned off and could cause a safety issue.

Draft Inducer Motor, Flue and Pressure Switch — Gas Furnaces

The draft inducer motor causes toxic fumes to be sucked up into a vent pipe or flue and transported out of the home. This ensures that the toxic fumes created when the gas burns in your furnace aren't transferred into your home with the desired warm air.

The pressure switch works in conjunction with these parts. When the draft inducer motor is on, a vacuum is created that draws the unwanted fumes into the flue. The pressure switch senses the vacuum and allows gas to flow into the furnace when the vacuum is present. If the vacuum isn't present, the switch prevents gas from flowing into the furnace because it might create a safety issue.

Limit Switch — Gas and Electric Furnaces

Limit switches support an important safety precaution to help prevent fires or damage to furnaces. If temperatures within the furnace get too high, the limit switch causes the unit to shut down.

Note that this furnace parts list isn't comprehensive and highlights the most important gas and electric furnace parts. A professional technician can help you understand what HVAC parts may be need service on your furnace if your HVAC unit isn't working well.