Quick answer: To prepare your HVAC for wildfire season, set the system to recirculate indoor air instead of pulling in fresh outdoor air, seal up the house so smoke can't leak in, and get the right filter installed before smoke arrives. Then stock spare filters ahead of time and be ready to swap them more often once the air turns.
This is the setup piece, not the filter-shopping piece. If you want the breakdown of which rating catches what and how smoke behaves, our air filter for wildfire smoke guide covers that in full. Here we're focused on the things you do to your system and your house so that filter can actually do its job when the sky goes orange.
Set the system to recirculate, not fresh-air intake
This is the single most important move, and it's the one most people miss. Many HVAC systems and smart thermostats have a fresh-air or economizer setting that pulls outdoor air into the house. That's great on a clear day and a disaster during a fire, because it feeds smoke straight indoors before your filter ever sees it.
Before smoke season, find your fresh-air intake — often a damper on the return duct or a setting on a smart thermostat — and set the system to recirculate indoor air only. Close any manual fresh-air dampers. If you run a whole-house ventilation system or an economizer, learn how to shut it off fast, because during a smoke event, recirculate is the mode you want.
Seal the house
Your filter can only clean the air that's already inside. Every gap that lets smoke in is air your system has to fight all over again. Before a smoke event:
- Close and lock windows and doors; locking pulls them tighter against the seal.
- Weatherstrip drafty doors and windows, and add a door sweep on exterior doors.
- Close the damper on any wood-burning fireplace.
- Turn off kitchen and bath exhaust fans during heavy smoke — they pull outdoor air in to replace what they push out.
The tighter the house, the more your filtered, recirculated air stays clean instead of getting diluted with fresh smoke.
Get the right filter in place before the season
You want the correct filter installed before the first smoke, not scrambling once it arrives. The short version: run at least MERV 13 (the floor for fine smoke particles), step up to MERV 14–16 only if your system has the airflow for it, and add an activated-carbon layer if the smoke smell bothers you. We explain exactly why — and how to tell what your system can handle — in the wildfire smoke filter guide and the carbon filter guide. Confirm your exact size with Find My Filter so the one you install actually seals in the slot.
Stock spare filters before smoke season
When smoke is thick, filters clog fast — sometimes in days rather than months. The worst time to discover you're out is mid-event with the air quality index in the red. Buy your season's filters while the air is still clear.
Because our flat-rate shipping is the same whether you buy one filter or a three-pack, it costs nothing extra to grab a multipack of your exact size and keep a few spares on the shelf. Then you can swap the moment airflow drops.
What to do during an active smoke event
Once smoke is actually in the air, your job shifts from prep to maintenance:
- Keep the fan running on recirculate. A filter only cleans air while air is moving through it, so run the system (or the fan-only mode) so it keeps scrubbing your indoor air.
- Check the filter every couple of weeks, not by the calendar. Swap it the moment it looks loaded or airflow weakens. A caked filter chokes the blower right when you need it working hardest.
- Create a clean room. Pick one sealed room where people and pets spend the most time and keep it tightest.
Pre-season wildfire checklist
- Locate your fresh-air intake or economizer and learn how to switch to recirculate.
- Weatherstrip doors and windows and add door sweeps.
- Close the fireplace damper and note which exhaust fans to shut off.
- Install the right filter now — MERV 13 minimum, carbon if odor is a concern — sized with Find My Filter.
- Stock a multipack of your exact size so you never run out mid-event.
- Plan to check and swap filters every couple of weeks during active smoke.
Frequently asked questions
How do I prepare my HVAC for wildfire season?
Set your system to recirculate indoor air instead of pulling in fresh outdoor air, seal the house with weatherstripping and closed dampers, and get the right filter installed before smoke arrives. Then stock spare filters ahead of the season and plan to swap them more often once smoke is in the air.
Should I run my HVAC during a wildfire smoke event?
Yes, as long as it's set to recirculate indoor air, not to pull in outdoor air. Running the system on recirculate keeps pushing your indoor air through the filter, which pulls smoke particles out. Just make sure any fresh-air intake or economizer is closed so you're not feeding smoke into the house.
How do I set my system to recirculate?
Look for a fresh-air, ventilation, or economizer setting on your thermostat or a manual damper on the return duct, and switch it so the system uses indoor air only. On most standard thermostats the default heating and cooling modes already recirculate; the setting to watch for is any explicit fresh-air or economizer feature that brings outdoor air in.
How do I keep wildfire smoke out of the house?
Seal the envelope: close and lock windows and doors, weatherstrip gaps, add door sweeps, close the fireplace damper, and turn off exhaust fans during heavy smoke since they draw outdoor air in. The tighter the house, the less smoke your recirculated, filtered air has to fight.
How early should I get filters for fire season?
Before the first smoke. Filters clog fast during heavy smoke, so buy a multipack of your exact size while the air is clear and keep spares on the shelf. Because flat-rate shipping is the same for one filter or a three-pack, stocking up ahead costs nothing extra and means you're never caught short mid-event.
Get ready before the smoke rolls in. Start with Find My Filter to confirm your exact size, then browse all Ironside filters and stock up while the air's still clear. Built here. Breathe better.