How to Clean a Furnace

An in-depth guide to give your furnace a super thorough cleaning

Co-authored by wikiHow Staff

Last Updated: May 20, 2022

Cleaning your furnace is an important task to keep on your home maintenance schedule. A dirty furnace will burn higher amounts of electric and/or gas fuel as well as work less effectively than a clean furnace. There are 3 basic parts of your furnace that can be impacted by the presence of dirt: the filter system, the blower, and the heat exchanger.^{[1]
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Research source} You must know how to clean a furnace effectively and do so regularly if you want to extend the life of your current furnace and prevent costly repairs.

Part 1

Part 1 of 3:

Inspecting the Furnace Filter

1
Locate the access panel on the outside of the furnace. This is below the return-air duct, between the blower system and the duct. Usually, the filter is found inside the front of the furnace. You may need to unscrew the front panel from the furnace or remove it from hooks that hold it in place in order to access the filter. Your furnace filter may also have its own access door.
- Make sure to turn off the furnace and/or HVAC system before opening it.^{[2]
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2
Remove the filter by pulling it up and out of the tracks. Generally, the filter should come out quite easily. To prevent damage to the filter and/or furnace, don’t force the filter out. If it seems stuck, look carefully and see if anything (like dirt or debris) is blocking it.

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3
Inspect the filter for dirt or damage. If the filter appears dirty, it needs to be cleaned or replaced, depending upon the filter type.^{[3]
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- If you are unsure whether your filter is dirty, hold it up to the light, and look through it. If you cannot see the light, the filter is dirty and needs to be replaced. A dirty filter will circulate dirt and dust through your home instead of usable, clean air and will force your furnace to work harder to push air through the grime.
- If your filter is not disposable, it must be cleaned. First remove any dirt or loose particles. Generally, a mild soap and tap water can then be used to rinse and wash the filter.^{[4]
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- Make sure to let the filter dry thoroughly before putting it back in the furnace.
- Many furnaces use a disposable filter. If this applies to yours, take the old filter to a hardware or appliance store (or record the size and/or model number), and purchase a replacement filter of the same type or model.
4
Place the new or newly cleaned filter back into the furnace. Slide the filter back into the furnace so that it fits securely. Then close the access door or reapply the furnace’s front panel using the hooks or screws.
- If the filter doesn’t seem to fit properly, make sure that no dirt or debris is blocking it. If you have a new filter that doesn’t seem to fit right, double-check that you purchased the correct type or size.
5
Remember to inspect your filter regularly. Furnace filters will need to be cleaned or replaced three or four times a year. Set reminders on your calendar to inspect yours regularly. For instance, you can check your filter on the first day of each season of the year.

Part 2

Part 2 of 3:

Cleaning the Blower Assembly

1
Unplug your furnace. Make sure that all power sources that run to your furnace unit, including battery backup systems or electrically generated power, are unplugged.^{[5]
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2
Remove the front panel of the furnace. To clean the blower assembly, you will most likely have to remove the whole front panel, even if your furnace has an access door for cleaning the filter. To remove the panel, you may have to loosen the screws that hold the panel in place or take the panel off its supporting hinges.
3
Slide the fan unit out of the furnace.^{[6]
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Research source} Most fans are secured to the furnace by a track, which allows it to slide in and out easily. The fan may also be connected by wire connections. If so, make a note of where each wire connects to the fan before removing them. This will make it easier to reassemble the unit.
- You can wrap a small piece of tape around each wire and label it, to make reassembly easier—just make sure to remove the tape labels before reattaching the wires to the blower fan.
- Some fans are held in by screws or bolts; remove these with a screwdriver or ratchet in order to take the fan out. Keep the screws or bolts in a safe place so you won’t lose them before you are ready to put the fan back.
4
Clean the blower assembly. A mild soap, and water are usually sufficient for cleaning the blower, although a toothbrush may help you to clean the fan blades and the small spaces between them.^{[7]
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- The blower assembly is the component that pulls air in through the back of the furnace, pushes it out of the front, and creates the heat. If the blower assembly is dirty, your furnace will push dust and dirt out through the vent system of your home. Thus, it is very important to clean the assembly well.
5
Vacuum the assembly. Running a handheld vacuum on low power over the fan blades and belts will help ensure that all dirt is removed. If you do not have a vacuum, you can also wipe any belts clean with a damp cloth.
6
Put the fan blower assembly back into the furnace. Once the assembly is clean and thoroughly dry, slide it back onto its track so that it fits into the furnace again. If you had to disconnect any wires to remove the assembly, reattach them, making sure to connect them to the right location.
- Remember to plug your furnace back in and turn it on after cleaning the fan blower assembly.

Part 3

Part 3 of 3:

Cleaning the Heat Exchanger Block

1
Turn the furnace off. Unplug all power connections running to your furnace. If it is a gas furnace, you should also turn the gas off.^{[8]
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Clear any dirt off of the block. Use a brush to loosen the black build-up off of each chamber of the block. You can also use a damp cloth to remove this buildup.^{[9]
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Vacuum the block assembly. Using a narrow vacuum attachment, thoroughly clean all chambers of the heat exchanger block assembly.^{[10]
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Research source} Using a vacuum will help ensure that all of the debris you loosened off of the assembly is removed.
- Remember to plug your furnace back in and turn it on once you have finished cleaning and vacuuming the heat exchanger block.

Community Q&A

Question

Could dirt prevent a furnace from turning on?

Community Answer

Yes, dirt caught in the vent of the furnace could back up the system and eventually stop it from turning on.
Question

Can I vacuum the vent of a furnace?

Community Answer

Yes, try a shop vac from your local hardware store. Those work well.
Question

Why is my furnace pulling the filters apart and blowing dust into my home?

Community Answer

Sounds like there is not enough return air. The unit can only blow out as much as it can pull in, if there is not enough return air or the return vent is not large enough, the unit will pull harder on the filter. It will also be less efficient.