If your furnace is acting up this fall, check the filter before anything else. A clogged filter is one of the most common reasons a furnace runs poorly, overheats and shuts itself off. It takes two minutes to check and costs a few dollars to replace.
How often to change it
- 1-inch filter: every 1 to 3 months. These are the thin filters that slide into a slot next to the furnace or behind a return grille.
- 4- to 5-inch media filter: every 6 to 12 months. These sit in a dedicated cabinet on the side of the furnace.
- Pets, allergies, smokers or renovation dust: check monthly and change sooner when it looks gray.
- First weeks of heating season: check it once the heat has been running for a couple of weeks. A summer's worth of dust often shows up fast.
How to find your filter size
- Turn the thermostat off before you pull the filter.
- Find the filter slot near the blower, usually on the side or bottom of the furnace, or behind a return air grille in the house.
- Read the size printed on the cardboard frame (for example 16x25x1). Buy the same size.
- Install the new one with the airflow arrow pointing toward the furnace.
What a clogged filter can cause
- Weak airflow from the vents and rooms that never warm up
- The furnace short-cycling or shutting off on its high-limit safety
- Higher gas and electric bills for the same comfort
- More dust around the house
If a new filter doesn't fix it, the problem is likely somewhere else, like a dirty flame sensor, a failing blower motor or a blocked vent. Our furnace tune-up checklist covers what a technician checks, and our furnace service team can find the real cause. The Rescue Club at $19 a month keeps your system on a regular maintenance schedule.
Have a boiler instead?
Many older North Jersey homes heat with a boiler and radiators, which don't use an air filter at all. If your home has central AC, it still has a filter at the air handler, so keep changing it through the year. See our boiler and heating service page for boiler care.
- How often should I change a 1-inch furnace filter?
- Every 1 to 3 months for most homes. Check it monthly if you have pets, allergies or a lot of dust, and change it when it looks gray.
- How often should I change a 4-inch media filter?
- Usually every 6 to 12 months. Check it at the start of heating and cooling season and change it sooner if it's visibly dirty.
- Can a dirty filter stop my furnace from working?
- Yes. A clogged filter restricts airflow, which can make the furnace overheat and shut itself off on a safety switch. Replacing the filter is the first thing to try.
- Do you service furnaces in my town?
- We serve Bergen, Passaic, Morris, Essex, Hudson and Union counties. Call (866) 737-2830 to confirm your address.