To keep wildfire smoke out of your house, close windows and doors, run your HVAC on recirculation with the fan set to ON so air passes through the filter constantly, and use the highest-rated filter your system can handle (a MERV 13 pleated filter catches far more smoke particles than a basic one). Turn off whole-house fans and evaporative coolers, and add a portable HEPA air cleaner in your bedroom.
North County lives with fire season and Santa Ana winds. Even fires many miles away can push smoke into Fallbrook, Bonsall and the inland valleys for days. Fallbrook Heating & Air installs indoor air quality equipment, including ECOAIRE non-restrictive electrostatic filters and Honeywell electronic air cleaners, and services the systems that move your home's air. Here's how to use what you have.
What should I do when smoke arrives?
Check the air quality on AirNow, close up the house, and switch your system to recirculate filtered air. Set the fan to ON rather than AUTO, so the filter works all the time, not just when heating or cooling. Make sure the filter is clean, and turn off anything that pulls outside air in.
- Check air quality. AirNow.gov shows current air quality and smoke conditions by ZIP code.
- Close up. Shut windows, doors and the fireplace damper.
- Stop outside air. Turn off whole-house fans and evaporative (swamp) coolers. If your system has a fresh-air intake or economizer, close it or set it to recirculate.
- Run the fan. Set the thermostat fan to ON so air keeps passing through the filter.
- Check the filter. Start with a clean one, and check it every few days while smoke lasts.
- Add room cleaning. Run a portable HEPA air cleaner in the bedroom or main living area.
Does my HVAC system filter out smoke?
Only as well as its filter, and only while the fan is running. Basic fiberglass filters protect the equipment but catch little of the fine particles in smoke. Pleated filters with a higher MERV rating catch much more. The system also has to be recirculating indoor air, not drawing smoke in from outside.
Smoke is mostly very fine particles, the kind that get deep into lungs. That's why filter rating matters so much during fire season.
Should I use a MERV 13 filter?
If your system can handle it, a MERV 13 or similar high-efficiency pleated filter is one of the most effective upgrades for smoke. The trade-off is airflow: a denser filter can restrict air on some systems, which can reduce cooling, freeze the coil or strain the blower. Ask a technician before switching.
| Option | How well it handles smoke | Trade-offs |
|---|---|---|
| Basic fiberglass filter | Poor; mainly protects the equipment | Cheap, low resistance |
| Mid-range pleated filter | Moderate | Fits most systems |
| MERV 13 pleated filter | Good at fine particles | Can restrict airflow on some systems; check first |
| Deeper media filter cabinet | Good, with less airflow resistance than a thin high-MERV filter | Installed by a technician |
| Portable HEPA air cleaner | Very good in one room | Covers one room; pick a correctly sized, ozone-free model |
| Ozone generators | Not recommended | Ozone is a lung irritant; avoid |
Should I run my AC or furnace during smoke?
Yes, if it recirculates indoor air. Running the system with a good filter cleans your indoor air and keeps you comfortable with the windows shut. Avoid anything that brings in outside air while smoke is heavy. If it's mild out, you can run just the fan on ON to keep filtering.
Smoke often comes with heat, especially during Santa Ana events. A system that's already struggling may not keep up with the windows closed. If your AC isn't cooling, see our AC repair page.
Are portable air purifiers worth it?
Yes, as a complement to your HVAC filter. A portable HEPA air cleaner sized for the room adds steady cleaning where you sleep or spend most of your time. Choose one that doesn't produce ozone; California certifies air cleaners through CARB. Avoid ozone generators marketed as "purifiers."
How do I keep smoke from leaking in?
Close the biggest openings first: windows, doors, fireplace dampers and pet doors. Then look at smaller leaks, like gaps around doors and windows. Leaky return ducts in an attic or crawlspace can also pull in dirty air; sealing them helps with both smoke and energy bills.
Duct sealing is part of every equipment replacement under California's Energy Code. Learn more on our Title 24 duct testing page.
What should I do after the smoke clears?
Replace the filter, since it will have caught a lot of fine particles. Air out the house once air quality is good again, and rinse ash and dust off the outdoor unit gently with a hose, with the power switched off at the disconnect. If the system smells smoky afterward, a technician can check the coil and blower.
- Replace the HVAC filter.
- Rinse the outdoor coil gently with the power off.
- Clean or replace portable air cleaner filters as the manufacturer recommends.
- Check the system cools and heats normally.
Do Santa Ana winds cause the same problem?
Partly. Santa Ana winds bring hot, dry, dusty air and raise fire risk across North County, and they can carry smoke from fires far away. The same steps help: keep windows closed, recirculate filtered air, and check your filter more often, because dust loads it up quickly.
Santa Ana days are also hard on the outdoor unit. Dust and leaves pile up on the coil, and the system works harder in the heat. After a windy stretch, clear debris from around the unit and rinse the coil gently with the power off. If dust has packed the filter, change it before the next hot day.
Who is most at risk from smoke?
Children, older adults, pregnant people, and anyone with heart or lung conditions such as asthma are most sensitive to smoke. For them, a clean room with a portable HEPA cleaner and a well-filtered HVAC system matters most. Follow public health advice and your doctor's guidance on when to stay indoors or leave the area.
For whole-home options, see our indoor air quality page. Our tune-ups include filter checks, and our maintenance tips cover filter changes year-round.
Frequently asked questions
Should I run my AC during wildfire smoke?
Usually, yes, as long as it recirculates indoor air and doesn't bring in outside air. Close windows and doors, set the system fan to ON so air passes through the filter continuously, and use the best filter your system can handle. Turn off whole-house fans and evaporative coolers, which pull outside air in.
Does a MERV 13 filter help with wildfire smoke?
Often, yes. Higher-MERV pleated filters, including MERV 13, capture far more of the fine particles in smoke than basic fiberglass filters. But a denser filter can restrict airflow on some systems, which can reduce cooling or strain the blower. Ask a technician whether your system can handle one before you switch.
Is a portable air purifier better than an HVAC filter?
They work best together. Your HVAC filter cleans air throughout the house while the fan runs, and a portable HEPA air cleaner adds extra cleaning in the room where you sleep or spend the most time. Choose a model that doesn't produce ozone; in California, look for CARB-certified air cleaners.
Does my HVAC system bring in outside air?
Many central heating and cooling systems only recirculate indoor air, but some have a fresh-air intake, and some homes have whole-house fans or evaporative coolers that pull outside air in. If you're not sure how your system is set up, we can check it during a visit.