How to change an HVAC air filter

Before you start

Check the system and filter manufacturer instructions first. The replacement must match the dimensions printed on the existing filter or specified by the equipment. A higher filtration rating is not automatically better for every system; a filter that is too restrictive can reduce airflow. If the filter is inaccessible, the cabinet appears sealed, or you would need to remove equipment panels beyond the normal filter access, stop and use a qualified HVAC professional.

Change the filter in six steps

1. Locate the filter. Look behind a large return-air grille or in a narrow filter cabinet beside the indoor furnace or air handler. Some homes have more than one return filter.
2. Turn the HVAC system off. Use the thermostat or normal system control before opening the accessible grille or filter cover.
3. Record the size and direction. Photograph the old filter before moving it. Note all three dimensions and the arrow printed on its frame.
4. Remove the old filter. Open the grille or cover and slide the filter out carefully. Do not force a filter past wiring or equipment components.
5. Install the new filter. Use the same size and a type appropriate for the system. Point its airflow arrow in the same direction as the old filter—normally toward the blower, furnace, or air handler and away from the return-air side.
6. Close, restart, and record. Secure the grille or cover, turn the system back on, and write down the installation date, size, and filter type so the next replacement is easy.

How often should the filter be changed?

ENERGY STAR recommends checking the filter every month and changing it at least every three months, or sooner if it looks dirty. Heavy heating or cooling use, pets, smoke, construction dust, and the filter design can shorten the interval. The equipment and filter instructions take priority over a general schedule.

Common mistakes to avoid

• Buying by appearance instead of matching the printed dimensions.
• Pointing the airflow arrow toward the room instead of toward the equipment.
• Assuming one filter serves the whole home when the system has multiple filtered returns.
• Forcing a high-restriction filter into a system that was not designed for it.
• Leaving the filter cover loose or operating the system without a filter.

Frequently asked questions

Which way should the filter arrow point?

Toward the blower, furnace, or air handler—the direction air travels into the equipment. Match the old filter and follow the equipment manual.

What if I cannot find a filter?

Check the manual and look at large return grilles as well as the indoor equipment. Do not open sealed equipment compartments to search. A qualified HVAC technician can identify the correct location and whether the system needs a proper filter rack.

Can I install a higher-rated filter?

Only if the equipment and filter manufacturer say it is suitable. More filtration can also mean more airflow resistance, so ask an HVAC professional when the approved range is unclear.