Check your HVAC filter every month and change it at least every three months, or sooner whenever it looks dirty. That's ENERGY STAR's rule of thumb for a standard 1-inch filter. Pets, allergies, construction dust and long stretches of heating or cooling can bring it down to every month or two.
How often to change it, by situation#
| Your situation |
Check |
Expect to change |
| Standard 1-inch filter, no pets, light use |
Monthly |
Every 3 months |
| One or more pets |
Monthly |
Every 1 to 2 months |
| Allergies or asthma in the house |
Monthly |
Every 1 to 2 months |
| Renovation, sanding or wildfire smoke |
Weekly while it lasts |
As soon as it's grey |
| Thick 4- or 5-inch media filter |
Every few months |
Per the label |
| Second home or vacation property |
Each visit |
At least every 3 months |
These are starting points. The EPA's guide to air filters puts it plainly: many factors affect how fast filters get dirty, manufacturers typically recommend 60 to 90 days, and if a filter looks heavily soiled when you change it, change it more often. Let the monthly check set the real schedule for your house.
How to tell if your filter is dirty#
Pull it out and look at the side that faces into the return duct, away from the furnace. A new filter is white or off-white. A filter that's due has a grey or brown coat over the pleats, often with visible hair and lint. Hold a standard pleated filter up to a light: if you can barely see light through it, change it.
Other signs:
- Weaker airflow from the vents
- The system running longer to reach the set temperature
- More dust settling on furniture than usual
- A heating or cooling bill that jumps without a change in weather
ENERGY STAR's maintenance checklist says a dirty filter can raise energy costs and damage the equipment, leading to early failure. The filter protects the blower and coils as much as your lungs.
Finding the right filter#
The size is printed on the frame of the old one, as three numbers like 16 x 25 x 1. That's the nominal size. The real dimensions are often slightly smaller, so buy by the printed size, not by measuring with a tape.
Check where all your filters are. Some systems have one at the furnace or air handler. Others have one behind each return grille in a wall or ceiling. Some have both. Changing one doesn't mean you've changed them all.
Which MERV rating?#
MERV ratings measure how well a filter catches particles. The EPA says most furnaces and HVAC systems can take a MERV 13 filter without problems, and suggests going to MERV 13 or as high as your system's fan and filter slot allow. If you're unsure, the EPA advises asking an HVAC technician. The EPA also ties that compatibility to changing the filter regularly, so a MERV 13 filter still needs the monthly check.
Some stores use their own scales, FPR or MPR, instead of MERV. The EPA notes those are proprietary ratings, so compare the MERV number where the package gives one.
How to change an HVAC filter#
Carrier's filter-change instructions start with power, size and airflow direction. In practice:
- Turn the system off at the thermostat, or at the switch on or near the furnace.
- Open the filter door or return grille and slide the old filter out slowly so the dust stays on it. Note which way its arrow points.
- Check the size on the old frame matches the new one.
- Slide the new filter in with the airflow arrow pointing toward the furnace or air handler, the direction the air travels. It should sit flat without bending or leaving gaps around the edges.
- Close the door or grille and turn the system back on.
- Write the date on the edge of the new filter with a marker. Next month, you'll know exactly how old it is.
Bag the old filter before carrying it through the house. Keep a spare or two in the closet so a due date doesn't also mean a shopping trip.
Washable and thick media filters#
Disposable filters aren't made to be washed. Rinsing one damages the media, and it goes back in damp. Replace it.
Permanent washable filters exist. Clean them exactly as the maker says, and let them dry completely before they go back in.
Thick 4- and 5-inch media filters sit in a cabinet next to the furnace. They hold more dust and last longer than 1-inch filters, but they still need a look every few months, especially in a dusty house.
Filter changes aren't the same as servicing#
Changing the filter is your job. Inspecting the burners, coils, refrigerant and electrical connections is a technician's. ENERGY STAR recommends a pre-season check-up every year, with the cooling system checked in spring and the heating system in fall. If you've got weak airflow with a clean filter, water around the indoor unit, or a filter that's black after a couple of weeks, call a technician.
Those check-ups slot naturally into spring maintenance and your winter prep list.
UK and European homes#
Many UK homes heat with a boiler and radiators and have no air filter at all. If yours has mechanical ventilation with heat recovery (MVHR), or a ducted air conditioning or heat pump system, those do have filters, and the manufacturer's manual sets the cleaning or replacement schedule.
Staying on schedule#
The monthly check is the habit that matters. Set it as a repeating ChoreLists.com reminder, with a note of the filter size and MERV so you can reorder without pulling the old one out first. If you also run a portable purifier, its air purifier filters follow a separate schedule.