California Air Duct Pros guide
Wildfire Smoke, HVAC Filters, and Your Ducts: A California Guide
During wildfire smoke, your filter matters far more than your ducts. CARB and the U.S. EPA recommend a MERV 13 filter (or the highest rating your system can handle), recirculating indoor air instead of drawing in outdoor air, and changing filters more often. Duct cleaning isn't smoke protection, but it may be worth considering afterward if you find heavy dust or debris in the ducts or particles blowing from supply registers.
Updated October 19, 2026Sources listed below
Why this matters in California
NOAA's climate summary for California notes that summer is the dry season and wildfires are common, particularly toward the end of summer. Santa Ana winds, which can gust to 80 mph, are often associated with the most destructive fires, and 2020 saw a record number of acres burned.
That makes it worth knowing how to set up your heating and cooling system before smoke arrives, rather than during a smoky week.
Before and during a smoke event
CARB and EPA guidance lines up on a few practical steps for homes with central heating and air conditioning:
- Install a high-efficiency filter — MERV 13 or higher, or as high a rating as your system fan and filter slot can accommodate.
- If your system has a fresh-air intake, close it or switch to recirculate so it isn't pulling outdoor smoke inside.
- Set the fan to "on" rather than "auto" so air is filtered continuously (CARB).
- Keep spare filters on hand and expect to replace them more often than the manufacturer's usual schedule during heavy smoke (EPA).
- Check the filter frequently and change it when it appears dirty (EPA).
Sources: California Air Resources Board — Smoke Ready California; U.S. EPA — Wildfires and Indoor Air Quality
After the smoke clears: filter first, then the ducts
Start by replacing a smoke-loaded filter. Then look at your supply registers and return grilles. EPA suggests considering duct cleaning when ducts are clogged with excessive dust and debris, or when particles are actually released into the home from supply registers.
Be realistic about the benefit. EPA notes that duct cleaning has never been shown to actually prevent health problems, and it recommends cleaning ducts only as needed. Cleaning removes built-up material; it doesn't replace good filtration the next time smoke arrives.
Source: U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?
Be careful with add-on "air purifying" devices
California's air cleaner regulation (AB 2276) requires all indoor air cleaners sold in, or shipped to, California to meet ozone emission and electrical safety standards, with ozone emissions no greater than 0.05 parts per million. The regulation used to exempt electronic in-duct air cleaning devices; that exemption has been eliminated, and the phase-in period ended October 1, 2022.
If you're offered an electronic device for your ductwork, check CARB's list of devices that meet its standards before buying. For a portable room air cleaner, EPA recommends choosing one sized for the room that does not produce ozone.
Sources: California Air Resources Board — California's Air Cleaner Regulation (AB 2276); U.S. EPA — Wildfires and Indoor Air Quality
What a proper duct cleaning should include
If you do decide on cleaning, EPA suggests the provider agree to clean all components of the system and use vacuum equipment that exhausts particles outside the home or HEPA vacuuming equipment. EPA also notes that no products are currently registered as biocides for fiberglass duct board or fiberglass-lined ducts.
Cleaning is not repair. If ducts are damaged, disconnected, or leaking, that's work for an HVAC contractor — and in California, depending on the work, HVAC changes can require Energy Code field verification and diagnostic testing.
Sources: U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?; California Energy Commission — Home Energy Rating System (HERS) Program
Questions
Can I use a MERV 13 filter in any system?
Not always. EPA's advice is to use a MERV 13 filter or as high a rating as your system fan and filter slot can accommodate. If you're unsure, check your system's manual or ask an HVAC professional.
Will duct cleaning get rid of smoke smell?
Don't count on it. Start with the filter — EPA advises checking HVAC filters frequently during smoke and changing them when they appear dirty. If you can also see heavy dust or debris in the ducts, or particles coming from supply registers, that's one of the situations where EPA says duct cleaning may be worth considering.
Source: U.S. EPA — Wildfires and Indoor Air Quality; U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?