How to Change an HVAC Air Filter

Quick answer

Turn off the system, slide out the old filter noting the airflow arrow direction, insert a same-size replacement with the arrow pointing toward the blower, then restart the system. Most 1-inch filters are changed every 60–90 days—monthly if you have pets or allergies.

Changing your HVAC filter is one of the highest-return maintenance tasks: better airflow, lower energy use, and less dust on coils and in your home. It requires no special tools and takes minutes once you know where the filter lives.

Where to find the filter

Common locations:

If unsure, follow the large return duct toward the air handler—the filter is usually on that path.

Tools needed

• None required for most systems
• Screwdriver if return grille is screwed shut
• Flashlight for dark closets/attics

Materials needed

• Replacement filter matching size and thickness
• Optional: notebook to log change dates

Step-by-step replacement

1. Turn off the HVAC system — Set thermostat to OFF so the blower doesn't start while the filter is out. This prevents pulling unfiltered air and dust into the system.

2. Remove the old filter — Open the filter door or return grille. Note the arrow printed on the frame—it shows installed direction. Slide the filter out.

3. Check size and condition — Size is printed on the edge (e.g., 20x25x1). A dark, clogged filter confirms it was overdue. Vacuum loose dust in the slot if needed.

4. Install the new filter — Insert with the arrow pointing toward the blower (same as the old filter). The filter should sit flush without gaps around the frame.

5. Restore power and note the date — Close the door/grille, turn the system on, and write the change date on the filter edge or calendar. Set a phone reminder for 60–90 days.

MERV ratings (quick reference)

For a full selection guide, see what MERV rating to choose. Quick reference:

Higher MERV isn't always better if your system can't move enough air. When in doubt, use the manufacturer-recommended type.

How often to change

See our filter change schedule guide for household-specific intervals. Quick reference:

• Standard home: every 90 days
• Pets or allergies: every 60 days
• During heavy HVAC use: check monthly
• Vacation home: at start of each visit

For a personalized interval based on your filter and household, use our HVAC filter replacement schedule calculator.

If airflow still seems weak

After a new filter is installed correctly, weak airflow or hot/cold rooms may indicate a separate problem—dirty coils, blocked return vents, or duct issues. If the system short-cycles (turns on and off rapidly) or rooms stay uncomfortable, schedule an HVAC technician rather than stacking higher-MERV filters.

Where this fits in your maintenance routine

Filter changes belong on every spring, summer, and fall checklist. If cooling struggles after a fresh filter, see why AC is not cooling before assuming a major repair. Pair with furnace maintenance before heating season and testing smoke and CO alarms when you do seasonal walkthroughs.

Bottom line

Changing the filter is beginner-friendly, inexpensive, and worth doing on a predictable schedule. It is not a substitute for professional service on gas combustion systems, refrigerant repairs, or persistent comfort problems.