Dirty AC or furnace filters are the number one problem when forced-air heating and cooling systems don’t work right.

With a central forced-air heating and cooling system, heat-pump, furnace or AC air filters remove dust and allergens from the air before warming or cooling air and returning it to your rooms. For this reason, filters are critical components of these systems. But, on the downside, as AC, heat-pump, or furnace filters become clogged with dust and debris, they block the free flow of air, drastically reducing the system’s efficiency. This can cost you a lot of money over the long run.

Also read: 5 Ways to Save Money on Your Heating Bill Now

Properly maintaining furnace or AC filters is an important way to keep your heating and cooling as affordable as possible. Clean permanent filters or replace disposable forced-air system filters every six months unless they become clogged with dust sooner.

Filters are typically located at the home’s ceiling or wall return-air registers, and/or they may be placed in the furnace or AC unit’s air-handler cabinet.


Man’s hand removing an air conditioner filter on a wall return-air register.
Position the replacement filter in the wall register with the airflow arrows pointing in toward the ductwork. ©Don Vandervort, HomeTips

Before beginning filter replacement, turn off the heating or cooling system. After you locate replaceable filters, note the sizes marked on their frames or measure their sizes. Find your size of furnace filter on Amazon now.

Size measurements marked on a filter frame.
Keep images of your home’s filter sizes on your cell phone for reference when buying replacements.

How to replace a filter in a room’s return-air duct register:

1 Unlatch the register’s cover grille and swing it out of the way or remove it.

Note: On many registers, the “hinge” is made to come apart, so be careful that the grille doesn’t detach and fall off.

Remove the old filter and immediately put it in a trash bag or the outdoor trash.

Man removing a furnace filter out from a room's ceiling return-air register.
Carefully unlatch grille’s cover and remove the dirty filter. Steve Heap / Shutterstock.com

2 Clean dust off of the return-air’s grille before installing the replacement filter. Use a damp rag to clean the grille and the surfaces of the register—both inside and out. Again, be careful: The grille’s hinge side may unlatch on some types!

Dusting off a cover grille on a room's ceiling return-air register.
Clean dust off of the grille. Steve Heap / Shutterstock.com

3 Position the new replacement filter in the register with the airflow arrows pointed in toward the ductwork. Replace the grille and latch it.

Mark the date on the filter’s frame so you’ll know when it’s time to change it. (The filter shown is being installed in a wall return-air register.)

New replacement filter inserted, with date marks and arrows pointing to ductwork.
Replace the filter with “air flow” arrow is pointing toward ductwork. Mark the date on the filter’s frame so you’ll know when it’s time to change it. ©Don Vandervort, HomeTips

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How to replace a filter in a furnace or air-handler cabinet:

Man's hands changing a furnace filter.
© Charles Knowles | Dreamstime.co

1 Turn off the power to the furnace or air handler. Look for the door or panel that conceals the blower; sometimes this is marked “Filter.” Lift this door or panel off of its holding hooks or unscrew its retaining screws to remove it.

Man lifting an air-handler cabinet's door.
Remove the air handler’s door (often by lifting it). Lennox

2 Check the filter. A standard filter is mounted next to or under the blower motor. Slide the filter out along its tracks.

Cut-away diagram of a furnace's internal and external parts, including filter, blower, and heat exchanger.
Furnace Parts Diagram

Check to see whether it is a disposable filter or intended to be cleaned and replaced—this should be marked on the filter’s edge, along with directions for cleaning, if applicable.

If it’s a disposable filter, its size will more than likely be printed on the frame’s edge. Find your size of furnace filter on Amazon now.

3 Buy a replacement filter and slide it into place, noting the arrows stamped on the side that indicate the proper direction of airflow; be sure you face these toward the blower (away from the ductwork). Then replace the door to the cabinet.

In the video below, Don offers good advice for changing furnace and AC filters:

Changing a furnace filter video shows how
Don Vandervort, HomeTips © 1997 to 2023 | HomeTips

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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” and served as MSN’s home expert for several years. Don founded HomeTips in 1996. Read more about Don Vandervort