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How to Replace Furnace & AC Filters

Dirty filters are the number one reason most HVAC systems begin to operate inefficiently.

©Don Vandervort, HomeTips

Position the replacement filter in the wall register with the airflow arrows pointing in toward the ductwork.

With a central forced-air heating and cooling system, air filters remove dust and allergens from the air before returning it to your rooms. For this reason, its filters are a critical component of the system.

But, on the downside, as filters become clogged with dust and debris, they block the free flow of air, drastically reducing the system’s efficiency. Properly maintaining filters is an important way to keep your heating and cooling as affordable as possible. Replace or clean the forced-air system filters every six months unless they become clogged with dust sooner.

Filters may be located at the return-air registers in the home or in the furnace or AC unit’s air-handler cabinet. In many cases, they are in both places.

The first step is to turn off the heating or cooling system and then locate the filters and measure their sizes (or note the sizes marked on their frames).


To replace a filter located in a room’s return-air duct register:

For a ceiling-mounted filter, unlatch the grille and lift out the dirty filter.Steve Heap /

For a ceiling-mounted filter, unlatch the grille and let it hang straight down (be careful not to disconnect its hinges). Pull out the dirty filter.

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1Unlatch the register’s cover grille and swing it out of the way or remove it. Remove the old filter and immediately put it in the outdoor trash. Use a damp rag to remove dust from the grille and the surfaces of the register—both inside and out.

Clean dust off of the grille.Steve Heap /

Clean dust off of the grille before installing the replacement filter.

2Position the new replacement filter in the register with the airflow arrows pointed in toward the ductwork. Replace the grille and latch it.


To replace the filter in the air-handler cabinet:

1Turn off the power to the unit. 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.

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

Mark the date on the filter's frame so you'll know when it's time to change it. Note: Be sure the "air flow" arrow is pointing in the right direction.©Don Vandervort, HomeTips

Mark the date on the filter’s frame so you’ll know when it’s time to change it. Note: Be sure the “air flow” arrow is pointing in the right direction.

3Buy 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.

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Join the Conversation

  • dave gartner

    My heat pump was inspected 1 month ago.The tech said coolant level was good.Unit was iced up this AM.Outdoor temp 76 F.The unit was re-charged 2 years ago,same symptoms.Whats going on?

  • Don

    Dave, normally I would tell you to check the filters, but they’re probably fine if it was recently inspected. If you suspect that they could be dirty, clean or replace them. Make sure nothing is restricting air flow. Turn off the unit long enough for the ice to melt. Then try it again. If this doesn’t work, call the AC repair person who came out before and discuss the issue on the phone, if possible. Hopefully, he’ll give you a little free time since you paid him recently. There could be a problem with the blower.

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