How do you keep the air inside your home clean during a smoke event?

Start by sealing up your house. Shut the windows and doors, and set any air conditioner to recirculate so it isn't pulling smoky air inside[1]. Sealing helps, but it doesn't make the air clean. With everything closed, indoor smoke still sits at roughly 55 to 60% of the level outside, but that varies a lot from home to home[1]. If you leave a window open the air inside is about as dirty as the air outside[1].

To clean the air, you have to filter it. In a forced-air heating or cooling system, fit a MERV 13 or higher filter and set the fan to ON so it runs nonstop[1]. A portable air cleaner does the same for one room, cutting indoor smoke by around 65% on average[1]. No system or air cleaner? Tape a MERV 13 furnace filter to a box fan for a cheap cleaner that works nearly as well[1][2]. Just use a fan built since 2012 with a UL or ETL mark; older ones were not tested for this and pose a fire risk[1][2]. Change any filter often, because a dirty one barely cleans[2].

You can also stop adding smoke of your own. Frying or broiling, burning candles or incense, spraying aerosols, and smoking or vaping all add fine particles to the air indoors[1]. Skip vacuuming during a smoke event too, unless your vacuum has a HEPA filter[1]. Avoid electronic air cleaners: EPA doesn't recommend them for smoke and says to use only CARB-certified models[1]. If cleaning the whole house is too much, set up one cleaner air room instead. Pick an interior room with few windows and doors, like a bedroom, and run your cleaner where you sleep[1].

In one situation, sealing works against you. Sealing the house in hot weather raises your risk of heat stress, and the danger is worse in a home without air conditioning[1]. If you have no AC and it turns dangerously hot, open the windows and doors at night when the air is cooler, even if some smoke gets in. Close up and filter again once the house has cooled[1]. When that isn't enough, go where the air is both cool and clean: a friend's home with AC and a filter, or find somewhere with cleaner/cool air like a mall, library, or cooling center[1].