How to replace a furnace filter

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In the video, Brian slides a new 3M filter into the furnace. It is one of the easiest jobs in the house, and one of the most skipped.

Video by Brian Huie on YouTube. Watch on YouTube

How often
Every 3 months (check monthly)
Video
23 seconds

How often should you change a furnace filter?

Check the filter every month and change it at least every three months, or sooner if it looks dirty. The EPA suggests changing it more often if old filters come out heavily soiled.

How do you replace it?

  1. Turn the system off.
  2. Slide out the old filter and note its size, or snap a photo of it.
  3. Insert the new filter with the arrow on the frame pointing toward the furnace, in the direction of airflow.
  4. Make sure it fits snugly so air cannot slip around it, then turn the system back on.

Which filter rating should you buy?

Higher ratings catch more particles. The EPA recommends a filter rated at least MERV 13, or as high as the system allows, and notes that most furnaces can take a MERV 13 without problems. FPR and MPR are brand-specific scales; MERV is the national standard.

Why does it matter?

ENERGY STAR says a dirty filter can raise energy costs and damage the equipment, leading to early failure.

Safety notes

  • Turn the system off before changing the filter.

Seattle-area notes

During wildfire smoke, the Washington Department of Health recommends a MERV 13 or higher filter and checking it at least monthly, more often in heavy smoke.

When to call a pro

Ask an HVAC technician which is the highest-rated filter the system can handle.

Related guides

Service your AC and furnaceHow to clean an air purifierAll Home Care Advice guides

Sources

  1. ENERGY STAR Homeowner Manual (PDF)
  2. EPA guide to air cleaners in the home
  3. Spire: how to change your furnace filter
  4. U.S. DOE Building America Solution Center: filter arrow
  5. ENERGY STAR maintenance checklist
  6. Washington Department of Health: wildfire smoke and HVAC filters

Checked October 2026. Manufacturer instructions for a specific model come first. General information, not a substitute for a licensed professional.

From the Home Care Advice by Brian Huie, a principal broker and Realtor with Compass in Seattle.