Symptoms
- Not a malfunction, but a maintenance question
- Unsure filters are being changed on the right schedule
Likely causes
- CommonStandard 1-inch filters clog fasterThin filters need replacement every 1–3 months in most homes.
- CommonPets or allergy sufferers in the homePet hair and dander clog filters faster, often needing monthly changes.
- PossibleThicker 4–5 inch media filters last longerThese can often go 6–12 months depending on the manufacturer's rating.
- PossibleConstruction, wildfire smoke, or heavy dust eventsThese can clog any filter within days or weeks and call for an off-schedule check.
What to do
- Check the filter packaging for the manufacturer's suggested interval as a starting point.
- Physically check the filter monthly during heating and cooling season by holding it up to light.
- Replace on a 1–3 month schedule for standard filters, or 6–12 months for thick media filters, whichever comes first based on visual dirt.
- Shorten the interval if you have pets, allergies, or recent construction or smoke exposure.
- Keep a few spares of the correct size on hand so replacement is never delayed.
- Write the install date on each new filter to make tracking effortless.
Tools and parts
Furnace air filter, correct sizeSearch: “furnace filter size MERV replacement”
When to call a pro
Not typically needed; ask an HVAC technician for a filter recommendation during a routine maintenance visit if unsure which type fits your system.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.