Filters for wildfire smoke
When the sky turns orange, the filter does the work.
A central system can clean the air in every room it serves, if the filter is right and the fan keeps running. Here's what EPA and the state's air board say to do, and what to avoid.
The filter
Choose a high-efficiency filter: MERV 13, or as high as your system can handle. Whatever the rating, it has to fit snugly so air doesn't leak around it.
How high your system can go depends on its fan and its filter slot, and an HVAC technician can tell you.
Source: U.S. EPA, Reduce Your Smoke Exposure. Rules and programs change: last checked 2026-10-22.
Source: U.S. EPA, Wildfires and Indoor Air Quality. Rules and programs change: last checked 2026-10-22.
Running it while the smoke lasts
With central air or a forced air furnace, run the fan continuously so the filter keeps catching fine particles. If the system has a fresh air intake, close it; that's sometimes called recirculate mode.
Expect to change filters sooner. EPA says replace them when they're dirty, which may be more often than the manufacturer recommends.
Source: U.S. EPA, Reduce Your Smoke Exposure. Rules and programs change: last checked 2026-10-22.
The whole house, or one room
Most HVAC filters clean the air throughout the area the system serves; a portable air cleaner is made for a single room.
If you buy one, California's air cleaner rule caps how much ozone it may give off.
Source: U.S. EPA, Wildfires and Indoor Air Quality. Rules and programs change: last checked 2026-10-22.
Source: California Air Resources Board, Indoor Air Cleaners and Wildfire Smoke FAQ. Rules and programs change: last checked 2026-10-22.
Ask before you upgrade the filter
Tell us the system and the filter size printed on the one you have, and we'll tell you how high it can go.
Do or don't
Smoke-day choices, sorted
What EPA and the California Air Resources Board say about each.
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Running the fan nonstop
It keeps the air moving through the filter while the smoke lasts.
Source: U.S. EPA, Reduce Your Smoke Exposure, checked 2026-10-22.
Do
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Recirculate mode
Close the fresh air intake on a system that has one.
Source: U.S. EPA, Reduce Your Smoke Exposure, checked 2026-10-22.
Do
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A finer filter than the last one
Ask first: what your system can take depends on its fan and filter slot.
Source: U.S. EPA, Wildfires and Indoor Air Quality, checked 2026-10-22.
Ask first
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An electronic in-duct air cleaner
Since October 2020, electronic in-duct air cleaning devices fall under CARB's air cleaner rule.
Source: California Air Resources Board, Air Cleaner Information for Consumers, checked 2026-10-22.
Check it
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An ozone generator
CARB strongly advises against using one in the home, or any air cleaner it hasn't approved.
Source: California Air Resources Board, Air Cleaner Information for Consumers, checked 2026-10-22.
Don't
Tell us what it's doing. We'll take it from there.
Call and describe the problem: the noise, the smell, the room that never warms up. Or book a visit online.
