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Every furnace or AC uses a filter on the return side of the ductwork. Room air passes through this filter before the blower sends it back out. Once you know the common hiding places, finding it is quick. The steps below explain where to look and how to swap the filter without fuss.
Look for the biggest grille in a hallway wall, floor, or ceiling. Many homes hide the filter right behind that grille. Flip the latch or remove the two tiny screws and pull the filter straight out.
If there’s no filter behind the return grille, find the indoor unit, the metal box that holds the blower. On the side or bottom is a slim slot with a small cover. Lift off the cover and the filter will be right behind it.
If the unit hides in a basement, attic, or small closet, builders often add small filters behind each return vent so you don’t have to crawl into the equipment.
Some newer houses return air only through ceiling grilles. Each grille has its own filter. Push two tabs, swing the grille down, and remove the filter.
Energy experts recommend checking the filter every month and replacing it within one to three months, or sooner if it looks gray.
Let a washable filter dry completely before sliding it back in. A damp filter can grow mold. A damp filter can grow mold.
Spend five minutes to spot every filter in your home. Mark each location, set a monthly reminder, and change or clean the filters on schedule. This quick habit keeps your air cleaner, your rooms comfortable, and your energy bills lower.
Most filters sit either behind the largest return grille (a vent on a wall, floor, or ceiling) or inside a thin slot on the air-handler or furnace cabinet. Start with the grille; if it is empty, check the slot by the blower.
Walk around and open every return vent you see. Bigger houses and ceiling-return systems often use two or more smaller filters instead of one big one.
On horizontal furnaces or air handlers—units that rest on their sides—the filter usually slides into a rack at the intake end of the cabinet. Look for a narrow cover held on by clips or a single screw.
Vertical units hide the filter below or above the blower section. Pull off the small access door on that side; the filter frame will be right behind it.
Find the arrow on the frame. Arrow toward the blower is the rule. Air flows from the return grille through the filter and into the blower.
If you have a forced-air furnace, heat pump, or central AC, you have at least one filter. Homes with only baseboard heat or window A/C may not.
Yes. Turn the thermostat to “Off,” slide the old filter out, note its size and arrow, and slide a matching one in the same direction.
Energy-saving guides from DOE and EPA say look once a month and replace or wash the filter every one to three months, sooner if it turns gray.
Some builders place filters in the ceiling returns when the furnace sits in a hard-to-reach attic or closet. This keeps service simple—just drop the grille and swap the filter.
