How-to
How to Change a Furnace Filter (and How Often)
🇩🇪 Diesen Artikel auf Deutsch lesenMost 1-inch furnace filters should be replaced every 1–3 months; thicker 4–5 inch media filters last 6–12 months. Turn the system off, slide out the old filter, check the size printed on its frame and insert the new one with the airflow arrow pointing toward the furnace.
Your forced-air furnace and central air conditioner pull all their air through one filter. When it clogs, the blower works harder, efficiency drops and parts wear out faster. Replacing it is the easiest maintenance task in the house.
Step by step
- Turn off the system
Switch the thermostat to off so the blower doesn't pull dust into the system while the filter is out.
- Find the filter
It is usually in a slot between the return duct and the furnace, or behind a return air grille on a wall or ceiling.
- Note the size and direction
The size is printed on the frame, for example 16x25x1. Note which way the airflow arrow points.
- Insert the new filter
Slide it in with the arrow pointing toward the furnace (in the direction of airflow). Make sure it fits snugly without gaps.
- Turn the system back on
Set the thermostat to heat or cool as before.
- Set a reminder
Write the date on the filter frame and set a phone reminder for the next change.
How often to change it
| Situation | Typical interval (1-inch filter) |
|---|---|
| No pets, no allergies | Every 2–3 months |
| Pets or allergies | Every 1–2 months |
| Construction dust or heavy use | Monthly |
| 4–5 inch media filter | Every 6–12 months |
Which MERV rating?
Filters are rated by MERV (Minimum Efficiency Reporting Value). MERV 8–11 is a good balance for most homes. Higher ratings catch finer particles but can restrict airflow on systems not designed for them — check your furnace manual before going above MERV 13.
Annual professional maintenance
A yearly tune-up checks burners, the heat exchanger, flue and safety controls. It keeps the system efficient and catches dangerous problems such as carbon monoxide leaks early. Make sure you also have working CO detectors on every floor.
Home Heating Cost CalculatorEstimate your yearly and monthly heating billTry the calculator →Frequently asked questions
What happens if I never change the filter?
Airflow drops, energy use rises, coils can freeze in AC mode and the furnace may overheat and shut down. Repairs cost far more than filters.
Are washable filters worth it?
They save buying replacements but usually filter less effectively and must be cleaned and fully dried regularly.