Wildfire Smoke and Your Home's Air: An LA Homeowner's Defense Plan
When smoke rolls over LA: close up the house, run your HVAC on recirculate with the best filter your system can safely handle, and add HEPA cleaning in the rooms you live in. Here's the full playbook, sourced from EPA guidance — including the MERV 13 caveat most articles skip.
By the Precise Air Systems, Inc. Team — reviewed by our senior technicians with 52 years of Los Angeles HVAC experience. Family-owned since 1975 · CA Lic #428900 · Mitsubishi Electric Elite Dealer.
The short answer: during a smoke event, keep doors and windows closed, set your HVAC to recirculate so it stops pulling in outdoor air, run the highest-efficiency filter your system can safely handle, and add portable HEPA cleaning in the rooms where you spend the most time. That is the consensus from the EPA's wildfire indoor air quality guidance — and it works, but only if your system and ductwork can actually execute it.
Why is wildfire smoke a special problem for LA homes?
Wildfire smoke is dominated by fine particulate matter — PM2.5, particles 2.5 micrometers and smaller — which penetrates deep into lung tissue and slips through the gaps ordinary homes and ordinary filters leave open. LA's fire seasons put whole neighborhoods under hazardous air for days at a time; you can watch conditions in real time on the AirNow Fire and Smoke Map, which shows PM2.5 readings block by block.
What should I do the day smoke arrives?
- Close everything. Doors, windows, and fireplace dampers. The EPA's smoke-and-heat preparedness guidance is blunt: keep the envelope shut while outdoor air is hazardous.
- Set HVAC to recirculate. If your system has a fresh-air intake or you run an evaporative (swamp) cooler, that path must be closed or filtered — otherwise you are actively importing smoke.
- Run the fan with a high-efficiency filter. A filter rated MERV 13 or higher meaningfully removes smoke fine particles as air cycles through the system.
- Clean, don't sweep. Settled ash gets airborne again with dry sweeping; damp methods keep it down.
Should I just install a MERV 13 filter? (The caveat that matters)
Only if your system can handle it. Here is what most articles skip: higher-MERV filters add airflow resistance (static pressure). Dropping a dense MERV 13 filter into an older LA home's system that was designed around a builder-grade filter can choke airflow — cutting cooling capacity, stressing the blower, and in bad cases freezing the coil. The EPA itself notes that most systems can accommodate MERV 13, which means some cannot. The precise answer is a static-pressure measurement: we test what your blower and duct design actually support before recommending a filter upgrade, and if the ducts are the bottleneck, sealing and repairing the ductwork is often the higher-value fix — leaky return ducts pull smoky attic or crawlspace air straight into the house.
What actually cleans the air inside: the layered stack
| Layer | What it does during smoke events | Best fit |
|---|---|---|
| High-efficiency HVAC filtration | Whole-home fine-particle capture on every fan cycle | Systems verified to handle the added static pressure |
| Portable HEPA air cleaners | Fast, room-level scrubbing where you sleep and live; EPA research on air cleaners for wildfire smoke supports HEPA-grade filtration for PM2.5 | Bedrooms, home offices, nurseries |
| Whole-home air scrubbers | Active in-duct treatment of particles and odors between filter passes | Homes wanting always-on, whole-home coverage |
| Controlled ventilation | Measured, filtered fresh air after the event — instead of leaks and cracked windows | Tight homes that need fresh air without opening up |
| Duct sealing | Stops the system pulling unfiltered attic/crawlspace air in through return leaks | Older LA housing stock — extremely common issue |
What about after the smoke clears?
Replace the filter (it worked hard), ventilate the house with the cleaner outdoor air, and consider a filter/IAQ check if the system ran continuously through a long event. If you noticed rooms that never cleared or a smoke smell that lingers in the ductwork, that is a duct-leakage signature worth diagnosing properly.
Not sure which layers your home actually needs? Take the 60-second indoor air quality check, or have us assess it in person — we recommend only what your home needs, with transparent, upfront pricing.
Prefer a straight answer from a person?
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Frequently asked questions
What MERV rating do I need for wildfire smoke?
EPA guidance recommends MERV 13 or higher to capture smoke's fine particles effectively — but your blower and ductwork must be able to handle the added airflow resistance. Have static pressure measured before upgrading; if your system can't support MERV 13, pair the best filter it can handle with portable HEPA cleaners in occupied rooms.
Should my AC be on recirculate during a fire?
Yes. Recirculate mode stops the system from drawing smoky outdoor air inside. If you have a fresh-air intake or evaporative cooler, close or filter that path for the duration of the event, per EPA guidance.
Do air purifiers really help with wildfire smoke?
Yes — portable HEPA air cleaners measurably reduce indoor PM2.5 in the rooms they serve, and EPA research supports their use during smoke events. They complement (not replace) whole-home filtration: HEPA units scrub the rooms you live in fast, while the HVAC filter cleans the whole volume more slowly.
Why does my house still smell like smoke days later?
Usually some combination of particles settled into fabrics, a spent filter, and duct leakage that keeps reintroducing attic or crawlspace air. Replace the filter first. If odor persists, duct inspection and sealing is the structural fix — we can test and seal the duct system so it stops pulling unfiltered air in.
How do I know when LA air is safe to open windows again?
Check the real-time PM2.5 readings for your neighborhood on the AirNow Fire and Smoke Map. When the AQI returns to Good/Moderate, ventilating the house helps flush residual indoor particles.