Wildfire Smoke & Your HVAC in Los Angeles and Ventura Counties
An HVAC system with suitable filtration can help reduce indoor smoke particles, but the right settings depend on your equipment and the condition of your home. Cooling, filtration and outdoor-air ventilation are separate functions.
This guide covers smoke preparation, operating precautions and when to discuss an HVAC assessment for homes in the Los Angeles County Valley area, the 101 Corridor and Ventura County.
Last reviewed: November 2, 2026
Important Safety Note
Follow evacuation orders immediately. Do not delay leaving to change filters, adjust equipment or wait for a service visit. If you cannot stay safely cool indoors during smoke, seek a cooler location with cleaner air.
Can You Run Your AC During Wildfire Smoke?
Often, yes—when the home is safe to occupy, the equipment is undamaged, and suitable filtration and outdoor-air settings are in place. Running a compatible central-system fan can move indoor air through its filter. It does not make every smoke-affected building safe.
A home with substantial soot or ash inside requires a different approach. LA County Public Health advises against running the HVAC system before the bulk of indoor soot and ash has been cleaned up, because operation can redistribute it. For fire damage or significant contamination, arrange appropriate assessment and cleanup before restarting affected equipment.
The operating guidance below concerns an otherwise safe, undamaged home affected by outdoor smoke. It is not a restart procedure for fire-damaged or heavily contaminated property.
Prepare Before Smoke Arrives
Keep the equipment manual, filter size and replacement instructions accessible. Ask your HVAC provider which filter the system can support and whether it has an outdoor-air intake or a separate ventilation system.
Keep compatible replacement filters available and learn the relevant controls before an event. Identify a room where your household can remain comfortably cool and use a suitable portable air cleaner if needed. Household members with health conditions should discuss a smoke plan with their healthcare provider.
HVAC Settings and Filtration During a Smoke Event
Use a Filter Your System Can Support
EPA recommends MERV 13 or higher where the system can accommodate it, or the highest suitable rating for the equipment. MERV describes particle-capture performance; it is not a guarantee that all smoke will be removed.
Confirm the filter's dimensions, fit and airflow compatibility. Follow the equipment instructions when replacing it. Do not force an oversized filter into the slot, stack filters or assume a higher rating is automatically suitable.
Check filters frequently during smoke and replace them when dirty, following the equipment and filter guidance. Heavy exposure can mean more frequent replacement than your usual schedule. A filter may need replacement before its usual scheduled date.
Check Outdoor-Air Controls Separately From the Fan
If the system has a fresh-air intake, use its approved temporary recirculation or intake-control procedure during smoky conditions. Not every thermostat has a “Recirculate” setting. Setting the fan to “On” is not proof that an outdoor-air damper is closed.
For a suitable central system with an appropriate filter, EPA recommends operating the fan more continuously during smoke to increase filtration. Confirm how your equipment and any separate ventilation controls work before changing settings.
Do not seal combustion-air openings, exhaust flues or all building vents. Temporary smoke settings should not become permanent changes that disable required ventilation. Restore normal operation when outdoor conditions and local guidance allow.
Use Portable Filtration Where It Helps
A portable HEPA air cleaner can supplement central filtration or serve a room without it. Select an appropriate smoke clean air delivery rate, or CADR, for the room and follow placement instructions so air can circulate around the unit.
Choose a CARB-certified mechanical-filtration model and avoid ozone-generating devices. CARB certification addresses specified safety and ozone-emission requirements; it does not rate how effectively a product removes smoke.
Particle filters do not remove every gas or pollutant. Cooling the room, reducing smoke particles and eliminating smoke odor are not interchangeable results.
Reduce Smoke Entry Without Overheating the Home
Keep windows and doors closed during smoke when you can remain safely cool. Avoid adding particles indoors through smoking, candles or high-heat frying. Air out the home when outdoor air quality improves and local guidance supports it.
Window units, portable air conditioners and evaporative coolers need equipment-specific advice. Window units may have an outdoor-air damper; single-hose portable units can draw smoky air into the home through other openings. Evaporative coolers rely on outdoor air. Check the manufacturer's instructions and EPA's guidance rather than applying central-HVAC settings to every appliance.
If the available cooling setup cannot maintain safe indoor conditions while limiting smoke, use a cooler, cleaner location.
What to Check After the Smoke Event
Continue following local air-quality information. A clearer-looking sky alone is not a reason to disregard advisories. If you evacuated, follow official return instructions before entering the property.
Filters and Visible Contamination
Check the HVAC and portable-air-cleaner filters and replace dirty filters according to their instructions. A fresh filter is useful, but it does not establish that the equipment, ductwork or rest of the building is clean.
Do not dry-sweep, blow or casually vacuum ash around equipment. These actions can put particles back into the air. Follow public-health cleanup guidance and obtain professional help for substantial contamination. Avoid opening equipment cabinets or disturbing deposits inside ducts yourself.
Cooling Performance and Equipment Condition
Reduced airflow, a change in cooling performance, visible deposits or a persistent odor are reasons to discuss an assessment. They do not identify a failed component or prove that the indoor coil needs chemical cleaning.
An HVAC professional can evaluate accessible components and recommend work based on their condition. Depending on the findings, that may involve filter correction, cleaning, repairs or further investigation. Ask which components are affected, what supports the recommendation and whether the proposed method is suitable for the equipment.
Do not attach improvised screens or covers to an outdoor unit to address ash. Equipment clearances and manufacturer instructions still apply.
Ductwork and Cleaning Decisions
Smoke exposure does not automatically mean every duct needs cleaning or replacement. EPA recommends duct cleaning as needed, such as when excessive debris clogs ducts or particles are being discharged from supply registers.
Where leakage or damage is suspected, ask about the accessible supply and return ductwork and the source of the problem. A filter change, duct cleaning and duct sealing address different issues. No single procedure guarantees the removal of all smoke contamination from a building.
When to Ask for Professional Help
Contact an HVAC professional when:
- You cannot identify the appropriate filter or understand the ventilation controls.
- Cooling or airflow has changed after smoke exposure.
- You see deposits around accessible equipment or particles coming from supply registers.
- A smoke-related odor persists and its source is unclear.
- The system or building may have sustained direct fire damage or substantial soot and ash contamination.
For significant building contamination, you may also need a qualified restoration or environmental professional. An HVAC assessment concerns equipment and operation; it does not certify that indoor air or the entire property is safe to occupy.
Share your address, equipment details, whether the system was running, and any changes you noticed. Agree on the assessment scope before work starts. Immediate fire or medical emergencies require emergency services, not a routine HVAC appointment.
Follow Local Smoke and Air-Quality Guidance
Use current official information for your location. Smoke conditions can affect areas beyond a fire's immediate perimeter; a city name or distance from a past fire cannot establish today's exposure.
For a separate explanation of local climate, cooling demand and equipment sizing, see our climate guide.
Discuss Your HVAC Concerns With Wind Flow AC
Wind Flow AC provides heating and cooling repair, maintenance and installation across the Los Angeles County / Valley Area, the 101 Corridor and Ventura County. Our office is in Calabasas, and service extends beyond the West Valley.
Contact us to discuss your equipment, filter compatibility or performance concerns after smoke exposure. We can discuss the HVAC work needed without assuming that every system requires the same cleaning or replacement.
Calabasas, CA 91302
Saturday: Closed
Sunday: 8:00 AM–7:00 PM