Thursday, August 5, 2021

If we’re going to be stuck inside, let’s make sure our indoor air is actually cleaner than the outside air

And if you were in eastern Washington this past week, you were in the thick of it.

When the smoke gets that bad, the Washington State Department of Health recommends that you stay inside and close up windows and doors to limit your smoke exposure. Facing still more time stuck inside can be tough after so many of us have spent so much time at home during the COVID-19 pandemic, but it's one of the best options we have to protect ourselves from the health effects of breathing in smoke.

Along with keeping those doors and windows closed, there’s another key part of this—taking steps to filter and clean the air in your home. When there are extended periods of poor air quality, smoke can seep into your home. So, we need to do something to filter those smoke particles out of our indoor air.

The best filtration option will depend on the characteristics of your home, your health and the health of your family, and your price point. There are technical details involved with all of these options, so we’re assigning you some homework:

  • If you have an HVAC system installed, it can help clean the air throughout your home. Increase the filtration to a MERV 13 rated filter, or the highest rated filter your system will handle. Set your system to recirculate and close the fresh air intake.
  • If you don’t have a whole-house filtration system, try designating a room as a cleaner air space and spend as much time in there as possible during smoke episodes. Here are two options to filter air in a smaller space:
    1. HEPA Portable Air Cleaners - Use an air cleaner that is rated for the size of the room and choose a model that has a true HEPA filter. There are machines that can produce harmful by-products (ozone generators, electrostatic precipitators and ionizers, or negative ion air purifiers) so don’t use those and check if the cleaner is CARB certified. Consider the noise rating, as some can be quite loud.
    2. DIY Box Fan Filters - Build your own clean air filter using a standard box fan and a filter with a MERV 13 rating of the same dimensions. Here are a couple design ideas:

Also, don’t add to indoor air pollution when there is already outside air pollution to deal with. Avoid burning candles or incense, smoking, diffusing essential oils, broiling or frying food, and vacuuming (unless your vacuum has a HEPA filter) when air quality is bad.

It can be hard to adjust all our regular activities and stay indoors or in one room and succeeding may take some creativity. Check out this brochure for some ideas.

It’s also often hot when it’s smoky. To stay cooler: close curtains or shades during the day, use portable fans, stay hydrated, or take a cold bath or shower. If it’s still too hot in your home, go to an indoor place that is cooler, even for a few hours, or open windows when outdoor temperatures are cooler and take some of the above steps to filter the air.

For more information of how to keep your indoor air clean and other resources visit WA DOH’s Smoke from Fires webpage.

Bonus: There’s a shiny new version of the Smoke & Fires map above. You will hear more about it soon.


  1. I don't like the new "Forecast" overlay on the map. It adds nothing useful and blocks the map.

  2. bug report: the forecast date slider also scrolls the map. Firefox 90.0.2

  3. So grateful for this resource. Question: how many sq. ft. does a box fan typically keep clean?

    1. Research is still emerging about box fan filters, and since they're DIY and materials vary, we don't know how many sq. ft. they will typically keep clean. We recommend a smaller room, where you spend most of your time and you can keep windows and doors closed (it won't be as effective if smoke keeps entering the room). It cannot clean large rooms as well. Using a MERV 13 rated filter will also be more effective than a lower rating.


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