Furnace Filter Replacement
How to Change Your Furnace Filter
A clean filter takes minutes to swap and protects airflow, comfort, and the furnace itself. Here is where to find it and how to change it.
Last updated: October 16, 2026.
The furnace filter is the smallest part of your heating system and one of the most valuable. It catches dust before the blower and coil, keeps airflow easy, and keeps rooms even. A clogged filter does the opposite: it chokes airflow, strains the blower, and can shut the furnace down on a cold night.
This guide shows where the filter hides, how to swap it step by step, how to pick the right one, and how often to check it. You need no tools for most filters, and the whole job takes minutes.
Why the filter matters
Air returns to the furnace through return ducts, and the filter sits in that path. It traps dust, pet hair, and lint before they coat the blower and coil. A clean coil absorbs heat well, a clean blower moves air with ease, and rooms stay even.
A clogged filter reverses all of that. Airflow drops, the coil gets too cold in summer and too hot in winter, and the furnace works harder for less heat. The blower strains, parts wear faster, and the furnace may shut down on a safety control. A clean filter is the cheapest upkeep a furnace gets.
Find your filter
- in a slot on the furnace itself, often at the bottom or the side of the unit.
- in a filter cabinet on the duct near the furnace, with a latched door.
- in a return air grille on a wall or ceiling, behind a hinged cover.
- in a filter rack inside the blower compartment, behind the front panel.
- check the furnace manual for the exact spot when you cannot find it.
Change it step by step
- Turn the thermostat to off, so the blower stops while you work.
- Open the filter slot, cabinet, or grille cover.
- Slide the old filter out and note the size printed on the frame.
- Note the arrow on the old filter frame. It points toward the furnace, in the direction of airflow.
- Slide the new filter in with its arrow pointing the same way.
- Close the cover, set the thermostat back to heat, and confirm the furnace runs.
- Write the date on the new filter frame or on a note near the furnace, so you know when you changed it.
Pick the right filter
Match the size printed on the old filter frame, and match the slot when the old filter is gone. A filter that gaps at the edges lets dust slip past, and a filter that bows in the slot chokes airflow. A standard pleated filter suits most homes and traps dust well without choking the blower.
A thicker filter traps more dust but needs a slot that fits it. A thin filter fits a narrow slot but traps less. Ask us when you want a higher-grade filter, because a filter that is too dense for the blower can cut airflow as badly as a dirty one.
How often to check
Check the filter monthly in winter, when the furnace runs daily, and monthly in summer when the AC runs. Homes with pets, construction dust, or a smoker in the house clog filters faster. Hold the filter to the light: if you cannot see light through it, swap it.
A yearly Maintenance & Tune-Up includes a filter swap and a check of the blower, coil, and ducts. Our Furnace Repair & Installation team can show you the filter location on your unit during any visit.
Further reading: The U.S. Environmental Protection Agency air cleaner guide explains filters, air cleaners, and indoor air basics. U.S. Environmental Protection Agency air cleaner guide
Frequently Asked Questions
Most filters sit in a slot on the furnace, in the return air grille, or in a filter cabinet on the duct. Check the furnace manual or the return grille first.
The arrow on the filter frame points toward the furnace, in the direction of airflow. Match the arrow to the air moving into the unit.
No, unless the filter says it is washable. Standard pleated filters lose their shape and trap less dust after washing, so swap them for a new one.
The size prints on the old filter frame. Read the numbers off the frame or measure the slot before you buy a replacement.
Dust coats the blower and coil, airflow drops, and the furnace works harder. Always run the furnace with a filter in place.