Can closing windows keep wildfire smoke out? How much smoke still gets in and do air purifiers work?

Breathing in polluted air makes you feel suffocated. You start feeling dizzy, your eyes burning and your skin irritating. You just want to get out of that area filled with smoke. So the first thing you decide to protect yourself from air pollution is that you shut the windows as smoke rolls into the neighborhood. Now what? You can close all the doors and windows you want, but however tightly you shut it, your home is still not going to airtight and some or many particles will enter your home. Fine particles from wildfires can still slip through small gaps as outdoor air leaks in. But you can’t actually predict the amount of pollutants getting inside your home and it totally depends on the area, homes and what kind of gaps are there in the room.

Researchers have been tracking a pollutant. It is a very fine particulate matter called PM2.5. The particles are so small that they can travel though the smallest gaps and still reach deep into your lungs.. Once PM2.5 gets indoors, a portable air cleaner can catch some of them and filter the air inside your room or house. How much air the machine has to clean depends partly on which doors are open.

Why does airflow matter for a portable air cleaner?

In a 2026 experiment, researchers at the National Institute of Standards and Technology (NIST) burned a mix of fuels outside a test house to simulate smoke from a fire where wildlands meet homes. They measured particle levels inside and tested different ways to lower them.


With interior doors open and the central heating and cooling system running, air mixed across the house. Under those conditions, the team found that air cleaners needed to be sized for the whole house. A machine rated for a bedroom could end up trying to clean a much larger volume of air.

The researchers also tried isolating a room. With the interior door shut and the room’s heating and cooling vents sealed for the experiment, one properly sized cleaner substantially lowered peak particle levels there. The experiment showed why a purifier’s room rating only tells part of the story. Air can move well beyond the room where the machine sits.

What did researchers find in Washington homes?

A separate study monitored households in King County, Washington, during the summers of 2023 and 2024. Researchers compared readings from indoor sensors with those from nearby outdoor sensors. Twelve households completed the study in the first year, and 24 did so in the second.

In 2024, both portable HEPA air cleaners and homemade box fan filters were linked to lower indoor PM2.5. After researchers accounted for outdoor particle levels, the estimated reduction was greater with HEPA units. The study was small, so it doesn’t tell you how much cleaner the air will get in your own home.

How can you set up a cleaner room during wildfires?

When there is a wildfire, what your instinct tells you to do is really the right choice which is to close your windows and doors. The U.S. Environmental Protection Agency also recommends you to do the same thing. They have suggested that you should select a room where you are most comfortable and spend time for long hours. Keep its windows and doors closed. After that you can run a portable air cleaner sized for the space which will filter the air particles polluting your home. When a wildfire situation arises outside, you should also avoid burning candles inside your home. Don’t fry food indoors while the air outside is still filled with smoke.

A closed room can get too hot. If you can’t stay cool at home, look for a cooler place with cleaner air. If local officials tell you to evacuate, leave as directed. An air cleaner is for times when it’s safe to stay indoors.

FAQs

Can smoke get inside even if I can’t smell it?

Yes. Use your local Air Quality Index rather than your nose to track outdoor smoke conditions.

Will one air purifier clean my whole house?

A unit sized for one room may struggle if air circulates through the rest of the house.