How To Change Your HVAC Filter

Locate Your HVAC Unit

Your central air handler or furnace is the heart of the system — and usually where the primary filter lives. Common locations include:

• Basement or crawlspace — the most common spot in older homes; look for a large metal cabinet near the water heater.
• Utility or mechanical closet — often a dedicated closet in a hallway, laundry room, or garage in newer construction.
• Attic — common in warm-climate homes where cooling is the priority; the unit sits on a platform above the insulation.
• Interior closet — townhomes and condos frequently hide a vertical air handler in a bedroom or hallway closet.

Tip: If you can't find it, follow the largest duct. Ducts radiate outward from the air handler like branches from a trunk.

Identify All Filter Locations

Many homes have more than one filter. There are two common arrangements:

• At the unit itself — a slot on the return-air side of the air handler (before the blower). This is almost always present.
• In wall or ceiling return-air grilles — large louvered grilles throughout the house that pull room air back to the unit. If a grille has a frame deeper than ¾ inch, it likely holds a filter. Hold your hand near it — if you feel suction, air is returning through there.

Tip: Walk every room and note all large vent grilles. Supply grilles (which blow air out) are usually smaller and won't have filters. Return grilles are larger, often 16×25 inches or bigger.

Turn Off the System

Before touching any filter, switch your thermostat to Off. This stops the blower from running while filter slots are open.

Why it matters: A running system creates strong suction at the return. Pulling a filter out while the blower is on sends a burst of unfiltered air — and whatever dust is on that old filter — straight through your ductwork and back into your living space.

Remove the Old Filter and Note the Size

Open the filter access panel or remove the return-air grille cover. Slide the filter straight out — they're not clipped in. Before you toss it:

• Read the three dimensions printed on the cardboard frame, e.g. 16 × 25 × 1 or 20 × 20 × 4. The third number is the thickness.
• Note the airflow arrow direction — you'll need to match it on the new filter.

Tip: Slide the dirty filter into a garbage bag immediately. Old filters are loaded with dust, pet dander, and sometimes mold spores — you don't want to carry it through the house open.

Choose the Right Replacement Filter

Match the exact dimensions — even a half-inch gap lets unfiltered air bypass the filter entirely. For MERV rating:

• MERV 8 — the standard choice for most homes. Captures dust, lint, pollen, and mold spores. Good balance of filtration and airflow.
• MERV 11–13 — better for allergy sufferers or homes with multiple pets. Captures finer particles but creates more resistance; confirm your system can handle it before buying.
• MERV 14+ — hospital-grade filtration. Avoid in residential systems unless your HVAC manufacturer explicitly supports it; the airflow restriction can overheat the motor.

Tip: If in doubt, check your HVAC manual or the sticker on the unit itself — many manufacturers specify a maximum MERV rating.

Install the New Filter

Slide the new filter in with the airflow arrow pointing toward the unit (toward the blower, away from the return-air space). The arrow should point in the same direction air flows — into the system.

• The filter should seat flush with no gaps around the edges.
• Close and latch the access panel or reinstall the grille cover.
• Write today's date on the cardboard frame with a marker — a quick visual check the next time you look at it.

Tip: If you have multiple filter locations, replace all of them in the same session. A clean unit filter paired with clogged wall-return filters still starves the system of airflow.

Set a Replacement Reminder

Turn the thermostat back on and set a recurring reminder so this doesn't become a "whenever I remember" task:

• 1-inch filters — every 1 to 3 months (lean toward 1 month if you have pets or allergies).
• 4-inch media filters — every 6 to 12 months.
• High-traffic homes (pets, smokers, heavy pollen seasons) — check monthly, replace as needed.

Tip: The easiest way to stay on schedule is to log the change in a home maintenance app like ManorKeep, which tracks your HVAC history and sends you a reminder when the next change is due — no calendar hunting required.