How to check the HVAC filter
Look at your HVAC filter once a month and change it when it looks heavily soiled. ENERGY STAR says to check monthly, and EPA says most makers call for a change every 60 to 90 days. Choose a filter that fits snugly, and aim for MERV 13 if your system can handle it.
How often to change an HVAC filter
Two official numbers apply here, and they answer different questions. ENERGY STAR tells you how often to look. EPA reports how often manufacturers say to replace. Your filter's packaging and your house decide the rest.
| Your situation | What to do |
|---|---|
| Any home | Inspect once a month |
| Typical replacement, per makers | Every 60 to 90 days |
| Filter looks heavily soiled when you pull it | Replace now, whatever the calendar says |
| MERV 13 or higher filter | Keep to the schedule. EPA says most systems handle these when they're changed often |
| Peak heating or cooling season | Look more closely. The system moves more air, so filters load faster |
| Pets, renovation dust or wildfire smoke | Check more often than monthly until things settle down |
Filters clean air only while the blower runs. EPA notes systems usually run less than 25% of the time during heating and cooling seasons, which is why the same filter lasts longer in a mild month.
HVAC filter size and MERV rating to look for
Pull the current filter and copy the size printed on its frame. Filters commonly come 1 to 5 inches thick. Buy one that slides in without bending. EPA warns that a loose or crushed filter lets air leak around the edges, so dirt gets past it.
The rating is the other thing to get right. MERV is the national standard. FPR and MPR are proprietary scales, so don't compare them directly with MERV. A higher number catches more of the small particles. EPA suggests at least MERV 13 or as high as your system can take. Filters at that level must remove at least 50% of the smallest particles tested.
- A replacement filter, or a few so you always have one on hand
- A marker to date the frame
- A vacuum with a brush for the grille
- A phone reminder set for the same day each month
HVAC equipment is rarely labeled with a filter limit. If you want a higher rating than the system came with, ask a technician at your next tune-up. A tech can tell you what your blower can handle and make changes if needed.
How to check your HVAC filter and swap it
- Turn the system off
Set the thermostat to off so the blower doesn't pull dust past an empty slot while you work.
- Find every filter
Check the air handler or furnace cabinet and any large return grilles. Note how many you have.
- Slide it out and compare
Look at both faces. Heavy gray or brown matting means it's time, even if the date says otherwise.
- Match size and rating
Copy the numbers from the old frame. Don't force a filter that's a little too big.
- Follow the arrow
Point the airflow arrow on the new frame toward the blower, which is away from the return duct.
- Date it and restart
Write today's date on the frame, close any panel fully and switch the system back on.
Signs of a dirty HVAC filter or a bigger problem
A dirty filter is normal. These problems are worth a closer look:
- Filter clogged within days of changing it. You may have a duct leak or a dust source nearby.
- Weak airflow at the vents even with a fresh filter.
- Rooms that won't reach the set temperature, or a system that runs longer than it used to.
- Dust on the blower side of the filter, which suggests air is getting around it.
- Ice on the indoor coil or the refrigerant lines in cooling season. Turn the system off and call a tech.
- A filter that's wet or moldy. Stop and have the system checked. EPA says not to run an HVAC system you know or suspect is contaminated with mold.
ENERGY STAR warns that a dirty filter can raise energy costs and damage equipment, leading to early failure. It also says airflow problems in general can cut a system's efficiency by up to 15%.
Check your HVAC filter yourself or call a tech?
Swapping the filter is always a DIY job. Most homes have it at the air handler, a return grille or both, and a house with two systems has two filters.
Bring in a licensed HVAC tech for anything past the filter: a dirty coil, a blower problem, frozen lines, duct leaks or a change to a thicker filter cabinet. If you have a gas furnace and smell gas, leave the house and call your gas utility from outside.
What homeowners say about when to change a furnace filter
A plumbing and HVAC tech gives rough intervals: 1-inch filters monthly, or every two weeks with pets, and 4- to 5-inch media filters every 3 to 6 months. Burning a lot of candles soots filters up fast. (Reddit)
Questions on how often to change an HVAC filter
How often should I change my HVAC filter?
EPA says manufacturers typically recommend every 60 to 90 days, and sooner if it looks heavily soiled. ENERGY STAR says to inspect it once a month.
Is MERV 13 too high for my furnace?
EPA says most furnaces and HVAC systems can use a MERV 13 filter without problems if it's replaced often. Equipment is rarely labeled, so an HVAC tech can confirm the best filter for yours.
Does a thicker HVAC filter last longer?
Follow the filter maker's interval for the exact size you buy. Filters come 1 to 5 inches thick, and your filter slot decides which thickness fits.
What you’ll need
Sources: ENERGY STAR, EPA
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.