How Often Should You Change
Your Furnace Filter?

Once the furnace starts running for the season, the filter becomes the hardest-working part of your heating system that you can service yourself. It's also the one most often forgotten. A clogged filter is behind a surprising number of winter no-heat calls we see in Kaysville, Bountiful and across Davis County, and it's the cheapest fix in your house.

The short answer

• Standard 1-inch filters: replace every one to three months. During winter, when the furnace runs the most, check it every month.
• Thicker 4- or 5-inch media filters: these last longer, often six months to a year. Follow the manufacturer's interval printed on the filter or cabinet, and still check them mid-winter.
• Change sooner if you have pets, someone in the house has allergies, you're doing a remodel, or the filter simply looks gray.

The real rule: if you hold the filter up to a light and can't see light through it, it's done, no matter what the calendar says.

Why winter is hard on filters here

In January your furnace may run for long stretches day and night, and every minute it runs, it pulls the whole house's air through that filter. Homes are closed up, so dust, pet hair and cooking particles have nowhere else to go. Holidays bring more people and more activity indoors. And Wasatch Front inversions are a good reason to keep filtration working at its best when outdoor air quality is poor.

Newer homes aren't exempt. Construction dust from finishing work or nearby building can load a brand-new filter in weeks.

How to check your filter in two minutes

1. Turn the system off at the thermostat so the blower isn't pulling on the filter while you work.
2. Find the filter. It's usually in a slot on the side of the furnace near the blower, in a media cabinet attached to the furnace, or behind a large return-air grille in a wall or ceiling.
3. Note the size printed on the frame (for example 16x25x1) so you buy the right one. A filter that's too small lets air, and dust, go around it.
4. Hold it up to a light. Gray, matted or no light coming through means replace it.
5. Install the new one with the arrow pointing toward the furnace, in the direction the air flows.
6. Write the date on the frame with a marker so you know when it went in.

Want to see it done? Watch our quick tip video further down this page, and find more maintenance help on our HVAC maintenance page.

Which filter should you buy?

Filters are rated by MERV, a scale that describes how well they catch particles of different sizes. Higher numbers catch finer particles, but they also make the furnace work harder to push air through.

• Cheap fiberglass filters mostly protect the equipment and do little for the air you breathe.
• Pleated filters in the MERV 8 to 11 range are a solid choice for most homes and most furnaces.
• MERV 13 and above catch finer particles like smoke, but a thick, high-MERV filter jammed into a 1-inch slot can choke airflow on a system that wasn't designed for it.

Higher isn't automatically better. Restricted airflow can make a furnace overheat and shut itself off on its safety limit. If you want better filtration for allergies or inversion season, the better route is usually a properly sized media filter cabinet or another whole-home option. Our indoor air quality page covers what's available.

Signs a dirty filter is causing problems

• The furnace runs a few minutes, shuts off, then starts again
• Weak airflow from the vents, or rooms farther from the furnace stay cold
• More dust settling on furniture than usual
• The furnace runs longer than it used to to reach the same temperature
• A furnace that won't run at all (start with our furnace troubleshooting guide)

If you replace a clogged filter and the problem continues, stop there and have a technician take a look. Repeated overheating isn't something to keep resetting.

A filter change isn't a tune-up

Changing your filter keeps air moving, but it doesn't tell you whether the burners are clean, the flame sensor is working, the heat exchanger is sound or the safety switches are doing their job. That's what a yearly furnace tune-up is for. Our $49 Safety & Operations Tune-Up is an easy way to get a licensed technician to look over your system before the coldest part of winter, and every visit ends with a written summary of what we found.

If you'd rather not keep track of it yourself, the Aireo Home Care Plan includes a furnace tune-up and an AC tune-up each year, plus a plumbing visit with a standard tank water heater flush and an electrical system evaluation.