The sky’s gone orange or gray, there’s a haze outside, and you can smell smoke even with the windows shut. What can you do right now to keep wildfire smoke out of your home?
The short answer: seal the house up, filter the air you’re breathing, and don’t add more pollution indoors. That three-part plan keeps your indoor air much cleaner than the air outside, and the steps below show you how.
Quick note before we start. This is general guidance, not medical advice. If anyone at home has asthma, a heart or lung condition, is pregnant, or is very young or elderly, talk with a doctor about a plan and follow your local health department’s advice.
How do you know when to act?
Wildfire smoke carries very fine particles that can get deep into your lungs, so it pays to check the Air Quality Index (AQI) for your area. In the US, AirNow.gov and many weather apps show current readings. As a rough guide, once the AQI climbs into the unhealthy range, it’s time to close up and run filtration.
Smoke can shift fast, though, so peek at the numbers a few times a day while the event lasts.
Close up the house
Keep windows and doors shut. If you’ve got a window air conditioner, or a portable unit with an exhaust hose, check whether it pulls in outdoor air. Then seal the obvious gaps with weatherstripping, or tuck a towel or some tape at the base of a door. You don’t need the house to be airtight, just less leaky.
Heat makes this tricky, because the urge to open a window is strong. Resist it. Run your air conditioning on recirculate if there’s a setting for it, and consider spending hot afternoons somewhere with clean, filtered air, like a library or a community cooling center, if one’s open.
Set up your HVAC for smoke
If you’ve got central heating and cooling, a few tweaks make a real difference:
- Set the system to recirculate indoor air instead of pulling in outside air, if it has that option.
- Install a higher-efficiency filter, such as MERV 13, if your system can handle one. Check the manual first, since a very dense filter can restrict airflow in some older systems.
- Run the fan on “on” rather than “auto,” so air keeps passing through the filter even when the system isn’t heating or cooling.
- Replace the filter more often than usual, because smoke loads it up quickly.
Make a clean room for wildfire smoke days
For most households, the most effective move is picking one room, usually a bedroom, and turning it into your clean air space. Keep the door closed, run a portable purifier with a true HEPA filter, and spend as much time there as you can, especially while you sleep.
Size matters here, because a purifier that’s too small for the room won’t keep up. Match the unit to the room’s square footage and check its smoke CADR, which we explain in our guide to choosing an air purifier by CADR, room size and filters. Ready to compare models built for smoke? Our roundup of the best air purifiers for wildfire smoke is the place to look, and if your clean room is a big open space, the best air purifiers for large rooms may suit you better.
A budget filter you can build
What if you can’t get a purifier? A do-it-yourself filter box is a well-known stopgap. People tape a furnace filter, usually MERV 13, to the front of a standard box fan, with the arrow pointing toward the fan. It moves plenty of air and costs little.
Use a newer box fan in good condition (older ones are a fire risk), never leave it running unattended, and keep it from tipping over or blocking walkways. A commercial purifier will usually be quieter and more convenient, but this can help in a pinch.
Don’t add to the problem indoors
Smoke days are the wrong time to make extra particles. Steer clear of these:
- Burning candles or incense, or using a wood fireplace
- Frying or broiling at high heat, which creates smoke and particles
- Vacuuming with a machine that lacks a good filter, since it can stir fine dust back into the air
- Smoking indoors
- Ozone generators and “air cleaners” that produce ozone, which irritates the lungs
If you cook, use the range hood when it vents outdoors, and pick gentler methods whenever you can.
Staying safe when you have to go outside
Ordinary cloth or paper surgical masks don’t filter out the tiny particles in smoke. A properly fitted N95 or similar respirator does a much better job, as long as it’s snug over your nose and mouth. Keep outdoor time short on bad days and skip heavy exercise outside.
When you come back in, consider changing clothes and rinsing off, since smoke particles cling to fabric and hair.
Get ready before smoke season
If wildfires are common where you live, a little prep goes a long way. Pick your clean room in advance, buy a purifier and a spare set of filters, stock a few respirators, and keep extra HVAC filters on hand.
A smart thermostat can help too, since you can set up the fan schedule ahead of time. Some models read temperatures from several rooms, which comes in handy if your clean room runs hotter than the rest of the house. Our roundup of the best smart thermostats with room sensors has options.
Frequently asked questions
Should I open the windows to air out the house after smoke?
Wait until the AQI outside has dropped back to a healthy level. Opening up too early lets the smoky air right back in.
Is a box fan filter as good as a purifier?
It’s a solid budget stopgap, but a commercial purifier is usually quieter and easier to live with. If you do build one, keep an eye on it and don’t leave it running unattended.
Do cloth masks protect against wildfire smoke?
Not really, because they don’t filter the tiny particles in smoke. A snug-fitting N95 or similar respirator is a much better choice.
The bottom line
You can’t control the air outdoors, but you can control a lot of what happens inside. For wildfire smoke at home, the winning plan is simple: close up, filter, and keep one room as clean as possible. Do those three things consistently and your indoor air will be far better than what’s outside.