Changing your furnace filter is the easiest thing you can do to keep your heating and cooling running well. It takes two minutes and costs a few dollars, yet a clogged filter is behind a surprising number of service calls. Here’s how often to change it, and how to tell when it’s time.
The short answer
It depends on the type of filter you have:
| Filter type | How often to change it |
|---|---|
| Thin filter (about 2.5 cm / 1 inch thick) | Every 1 to 3 months |
| Thick media filter (10 to 13 cm / 4 to 5 inches thick) | Every 6 to 12 months |
Check more often if you have pets, if someone in the home has allergies, or during renovations, when there’s a lot of dust in the air.
How to check your filter
- Turn the thermostat off.
- Find the filter slot. It’s usually where the large return duct meets the furnace, either on the side or the bottom.
- Slide the filter out and hold it up to a light.
- If you can’t see light through it, or it’s grey with dust, replace it.
Installing a new filter
Check the size printed on the edge of the old filter and buy the same size. Every filter has an arrow on the side: point the arrow toward the furnace, in the direction the air flows. Slide it in and turn the thermostat back on.
Why it matters
- Lower energy bills. A clean filter lets air flow freely, so your furnace and air conditioner don’t have to work as hard.
- Fewer breakdowns. A clogged filter makes the furnace overheat and shut off, and it can make your air conditioner’s coil freeze in summer.
- Longer equipment life. Less strain means less wear on the blower motor and other parts.
- Cleaner home. A good filter catches dust before it settles on your furniture.
From the field
Markham: a furnace that kept shutting off. The homeowner said the furnace would run a few minutes, shut off, then start again. The filter was packed solid with dust, so the furnace was overheating and the high-limit switch kept shutting it down. We put in a new filter, checked the limit switch and the temperature rise, and the furnace ran full cycles again.
Vaughan: an AC coil frozen in July. The AC was running with barely any airflow, and there was ice on the copper line outside. A dirty filter had choked the airflow and the indoor coil froze solid. We shut the system off to thaw, changed the filter, and checked the coil and refrigerant. It was cooling normally the next morning.
Aurora: a lower gas bill. The filter hadn’t been changed in over a year, and the furnace was running nonstop. We replaced it during a tune-up. The next month, the homeowner called to tell us their gas bill was noticeably lower and the house heated up faster.
It’s the cheapest fix in HVAC.
Make it a habit
An easy way to remember: check your filter whenever you get your gas bill, or set a reminder on your phone for the first of each month. Keep one spare filter beside the furnace, so you’re never caught without one.
Book a tune-up
A clean filter is a great start, but your furnace and air conditioner also need a professional check once a year. During a maintenance visit, we clean and inspect the system and catch small problems before they turn into breakdowns.
Air Net Heating & Air Conditioning provides furnace and AC maintenance across Richmond Hill and York Region, with upfront flat-rate pricing. Call 416-791-1609, open 8am to 8pm, 7 days a week.
Related service: Furnace and AC maintenance in Richmond Hill · Furnace repair in Richmond Hill