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What are Some Furnace Parts?

A furnace comprises critical components like the heat exchanger, blower motor, and thermostat, each playing a pivotal role in heating your home efficiently. Igniters, flame sensors, and filters also ensure safety and air quality. Want to understand how these parts work together to keep you warm? Join us as we break down their functions in detail.
Sherry Holetzky
Sherry Holetzky

While there are different types of furnaces, many heating systems function in the same basic manner. The four main types of furnaces include electric, gas, oil, and solid fuel. While the types of fuel differ, furnace parts tend to be similar. The basic furnace design begins with a thermostat. The thermostat gauges the temperature, which determines when the burner should be ignited.

An ignitor glows to light the burner, which simply put, burns fuel to create heat. More precisely, heated gas from the burner begins to raise the temperature inside the furnace’s heat exchanger. Heat exchangers are dual purpose furnace parts. They warm the air that is then distributed and they keep fumes created by burned fuel separated from the heated air that will be circulated.

Most furnaces contain the same basic parts.
Most furnaces contain the same basic parts.

Other furnace parts include the blower, which draws air in to be warmed as well as distributing warm air back into the space that needs to be heated. The air is moved through the duct work in each direction, cool air being drawn to the furnace through the return ducts while heated air is moved to the living space through supply ducts. The heated air leaves the duct and reaches the space via openings called vents or heat registers.

A thermostat will control the temperature setting of a furnace.
A thermostat will control the temperature setting of a furnace.

The fan limit switch keeps the blower from distributing air until it has been heated to the proper temperature. It also shuts off the burner if the temperature becomes too high. Thus, it prevents the furnace from running more than it needs to as well as acting as a safety feature.

Learning about basic furnace parts can give you the general idea of how a furnace works. Professional assistance is strongly recommended for furnace repair, but knowledge of fundamental furnace parts may be helpful in troubleshooting furnace issues or in performing light maintenance.

Most home furnaces also have a filter. The filter should be cleaned or replaced regularly. This is important not only to keep furnace parts clean and in optimum working order, but also to help filter the air that you breathe.

Furnace air filters need to be changed regularly as they can get clogged with allergens like pet dander.
Furnace air filters need to be changed regularly as they can get clogged with allergens like pet dander.

Another of the basic yet important furnace parts is the pilot light. It is often one of the first furnace parts checked when trouble is reported. Relighting the pilot light may prevent an unnecessary service call. If you don’t know how to light the pilot light, ask the repair person to show you how to do it safely and correctly on his or her next visit.

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Discussion Comments


the repair man says the rings are missing and said he had to tag it and couldn't turn it back on.


@cardsfan27 - Personally, I have to say electric furnaces are the best. I have never used propane, though.

A lot of people will say natural gas is cheaper than electricity, which is true if you are just looking at fuel cost. Any time I have used gas, though, there are always so many charges and different things tacked into the bill that it makes gas extremely expensive. Not to mention, on top of the bill, you one of the main gas furnace parts is the pilot light.

I don't know about you, but I have always hated dealing with pilot lights. I know it is supposed to be safe lighting them, but I always feel like I am going to turn the wrong knob or not set something where it is supposed to be and cause a fire or gas leak or something.

That is just my opinion, but I would try to find people with all different kinds and see what they think.


@JimmyT - For changing your furnace filter, I would suggest going with whatever the manufacturer says. They have designed that furnace for those standards for a reason. I know sometimes it can be hard to do, but it is worth it.

For my furnace, it takes two filters, and to replace them you have to reach up into the thing and put them at a weird angle. It's very difficult sometimes, but at least I always know I am breathing clean air. In the long run, your extra time and minimal cost for the filters should extend the life of your furnace, as well.


@JimmyT - I'm not sure exactly how a heat exchanger would work. My guess would just be that somewhere inside the furnace, the heat exchanger is just a thin piece of metal or something, so then the air that is heated by the fire and contains the fumes can heat that piece of metal which then heats the circulated air.

I am curious what people here think about the best type of furnace to get as a replacement. Our furnace is on its last legs, so we have the chance to get a different fuel type if we want. We pretty much have access to any power source - electric, gas, or propane. If there's one type that's easier to fine furnace replacement parts for, that's a plus.


Does anyone know anything more about how the furnace keeps the fumes away from the air that gets sent through the rest of the house? I never really thought about a furnace needing to do that until I read this.

It says the furnace uses something called a heat exchanger, but how exactly does this work?

Also, I am wondering what everyone's opinions are about how often you really need to change the air filter. The manual and filter packages and things like that usually say 3 months or something like that, but it never really seems to me like it needs to be that often. I usually just do it at the beginning of the cold season when I am just getting ready to turn the furnace on for the first time that year and at the beginning of summer when I start having to use the air conditioner.

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    • Most furnaces contain the same basic parts.
      By: scaliger
      Most furnaces contain the same basic parts.
    • A thermostat will control the temperature setting of a furnace.
      By: Mariusz Blach
      A thermostat will control the temperature setting of a furnace.
    • Furnace air filters need to be changed regularly as they can get clogged with allergens like pet dander.
      By: sushaaa
      Furnace air filters need to be changed regularly as they can get clogged with allergens like pet dander.