Quick answer
When wildfire smoke rolls into SW Washington, the goal is simple: keep smoke out, filter what gets in. Close up the house, run your HVAC fan with the best filter the system can handle — EPA recommends MERV 13 or as high as your system accommodates — set any fresh-air intake to recirculate, and add a portable HEPA cleaner for the rooms where you spend the most time.
- Fine particles (PM2.5) in smoke are the health concern — filtration is the countermeasure.
- EPA recommends upgrading to a MERV 13 filter, or as high a rating as your system can accommodate.
- Ventilation systems with fresh-air intakes should be set to recirculate during smoke events.
- A portable HEPA cleaner in the main living space backs up central filtration.
- Prepare in late spring: filter stock, system check, and a plan — not during the first smoky week.
What does wildfire smoke do to indoor air?
Smoke's harmful fraction is fine particulate matter — PM2.5 — small enough to slip indoors through every gap and to penetrate deep into lungs. During regional smoke events, indoor air in an unprepared house tracks outdoor air more closely than people expect. The EPA's wildfire and indoor air quality guidance is the authoritative playbook, and the current local conditions are always visible at AirNow.gov.
SW Washington's smoke seasons vary — some summers pass clean, others bring weeks of haze from fires that may be hundreds of miles away. The variance is exactly why preparation beats reaction: the equipment and filters you want are hardest to get during the event.
How should you run your HVAC system during a smoke event?
Four settings matter:
- Filter up. The EPA's home air-cleaner guidance recommends a MERV 13 filter — or as high a rating as your system can accommodate. Not every blower can handle MERV 13's pressure drop, so confirm before you swap (we can tell you in one visit).
- Run the fan. Air only gets filtered when it moves through the filter. Set the fan to ON or use a circulate mode during smoke events so filtration is continuous, not just when heating or cooling calls.
- Recirculate. If your system or HRV brings in outside air, switch it to recirculate mode so you're not importing smoke. (Restore normal ventilation after the event — tight homes need their fresh air back; see our ventilation guide.)
- Close the envelope. Windows, doors, fireplace dampers. Skip anything that pulls big outdoor volumes through the house.
Where do portable air cleaners fit?
Central filtration cleans the whole house slowly; a portable HEPA cleaner cleans one room fast. The EPA's recommended approach for heavy smoke is a "clean room" — pick the room where your household spends the most time, close it up, and run a properly sized HEPA unit there continuously. Size the unit to the room (manufacturers publish room-size ratings), skip anything marketed on ozone, and remember it only works with the door closed.
For households with asthma, young children, or older adults, the clean-room-plus-central-filtration combination is the difference between riding out a smoke week comfortably and breathing hazy air indoors for days.
How do you prepare before smoke season?
A late-spring checklist beats a smoky-August scramble:
- Stock filters — at least one spare at your target MERV rating; filters load up fast during smoke events and store shelves empty just as fast.
- Verify your system can take a higher-MERV filter — airflow testing tells you whether MERV 13 works or whether a media cabinet or duct correction is the better path (leaky return ducts also pull unfiltered air around your filter — see the duct guide).
- Service the system — a spring tune-up confirms the blower, coil, and controls are ready to run continuously if a smoke week demands it; our maintenance checklist covers the schedule.
- Know your recirculate settings — find the fresh-air damper or HRV mode now, not by flashlight during the event.
If you want a permanent upgrade, whole-house filtration and air-cleaning options integrate into the ductwork itself — our indoor air quality services cover what fits your system, honestly sized.
About this guide
Written and reviewed by the Home Energy Group team — a family-owned HVAC company celebrating 25 years of comfort & care across SW Washington and the Portland metro, licensed in Washington (WA LIC# HOMEEGI003J7) and Oregon (OR CCB# 184255), and an authorized Daikin & York dealer. Guidance reflects the systems we install and service every week. Last reviewed July 3, 2026.
Common questions
Should I run my AC during wildfire smoke?
Yes — run the system with the best filter it can handle and any fresh-air intake set to recirculate. Central AC and heat pumps recirculate indoor air by default, so running them filters your air and keeps the house closed up and comfortable at the same time.
What filter should I use during smoke season?
EPA recommends MERV 13, or as high a rating as your system can accommodate — higher-MERV filters catch the fine PM2.5 particles in smoke. The caveat: some blowers can't handle the added resistance, so confirm your system's limit before upgrading. We can verify it during a maintenance visit.
Do portable air purifiers actually help with smoke?
Yes — a properly sized HEPA unit meaningfully reduces fine particles in the room it serves. EPA's clean-room approach puts one in the room your household uses most, with the door closed, running continuously. Avoid ozone-generating devices.
Should I turn off my HRV during a smoke event?
Set it to recirculate if it has that mode, or pause fresh-air intake during the worst of the event — then restore normal ventilation afterward, because tight homes need continuous fresh air the rest of the year.
