Wildfire Smoke and Your HVAC: What to do when AQI spikes

Wildfire smoke can turn a normal day into a headache—literally. When air quality drops, your HVAC system can either help protect your indoor air or accidentally pull more smoke inside, depending on how it's set up and how it's used. Here's a practical, homeowner-friendly game plan for the hours and days when AQI spikes.

1) First, limit smoky outdoor air from getting inside

Smoke gets in through two main paths: open doors/windows, and the tiny leaks in every home (around doors, attic hatches, can lights, etc.). Your HVAC can't fix major air leaks on its own, so start with the basics:

• Keep windows and exterior doors closed
• Avoid running whole-house fans or window fans that pull outdoor air in
• Use kitchen/bath exhaust fans only as needed (they can depressurize the home and draw in smoky air)

If you have a fireplace or wood stove, don't use it during a smoke event.

2) Set your HVAC to "recirculate" when possible

The best move during a smoke event is usually circulating and filtering the air you already have indoors, rather than bringing in outdoor air.

If you have a furnace or air handler (ducted system)

• Set the fan to ON (or "Circulate" if your thermostat has it)
• This keeps air moving through your filter more often

If you have ductless mini-splits

• Mini-splits typically recirculate indoor air (they don't bring in outside air the way some ventilation systems do)
• Keep them running for comfort, but know: a typical mini-split doesn't filter smoke as effectively as a good whole-house filter + ducted system

3) Upgrade your filter (without over-restricting airflow)

Filtration is the biggest HVAC lever you can pull during smoke events.

Ducted systems: use the best filter your system can handle

A higher-efficiency filter can capture more fine particles, but if it's too restrictive it can reduce airflow and stress the system.

• If you normally use a basic filter, consider stepping up to a better pleated filter
• During smoke season, check filters more often and replace sooner if they load up quickly

Pro tip: The "best" filter is the one that balances filtration + airflow for your specific system. If you're not sure what's safe, ask your HVAC company what they recommend for your equipment.

Mini-splits: clean the washable filters

Mini-split filters are usually washable and great for dust, but they're not designed to capture smoke as well as high-MERV filtration. Still, keeping them clean helps efficiency and airflow.

4) If you have fresh-air ventilation, adjust it temporarily

Some homes have systems that intentionally bring in outdoor air, such as:

• ERVs/HRVs
• Dedicated fresh-air intakes tied to the HVAC system
• Certain whole-home humidifier or ventilation setups

During heavy smoke events, you may want to reduce or temporarily disable outdoor air intake, depending on your setup. The right setting depends on your equipment and indoor conditions—if you're unsure, it's worth a quick call so you don't accidentally create other issues (like moisture problems).

5) Add a portable HEPA filter for your "clean air room"

Even with HVAC filtration, a portable HEPA air cleaner can make a noticeable difference—especially in bedrooms.

Best practice:

• Pick one main room (often a bedroom)
• Keep the door closed as much as possible
• Run a HEPA purifier continuously while smoke is heavy

This is one of the fastest ways to improve comfort when AQI spikes.

6) Watch for these warning signs

Smoke events put unusual demands on your system. If you notice any of the following, it's time to reach out:

• System runs constantly but the home won't stay comfortable
• Burning smell, electrical smell, or unusual noises
• Excess dust/smoke smell that doesn't improve after filter changes
• Mini-split airflow feels weak even after cleaning filters
• Visible haze indoors

7) After the smoke clears: do a quick reset

Once air quality improves:

• Switch thermostat fan back to AUTO (if that's your normal setting)
• Replace the filter if it looks gray, dusty, or clogged
• Vacuum around returns and vents
• For mini-splits, wipe down and re-check filters

If your system struggled during the event, a maintenance visit can confirm airflow, filter fit, blower performance, and overall operation heading into the next weather swing.

Quick cheat sheet for smoke days

Do:

• Keep doors/windows closed
• Run a ducted system fan more often to filter air
• Use the best filter your system can handle
• Use a portable HEPA filter in a main room

Avoid:

• Whole-house fans or bringing in outdoor air
• Long runs of exhaust fans unless needed
• Burning candles/incense (adds indoor particulates)