How to keep your home smoke-free during wildfire season

This past week, fires and smoke have flared up in the West and the smoke is moving across the country. Air quality in many parts of the West is now (again) at miserable levels…


Fires and smoke have been dramatically increasing  in the last decade due to several factors. I’ll discuss that in a future blog post. But more urgently….this reminds me of a revelation I had in August of 2018. At that time, Seattle was suffering from its worst particulate air pollution ever due to many different fires throughout the Northwest. It was hot and smoky and miserable, but at least I could go home and go inside and get out of the smoke…or so I thought! Inside my house, I could smell smoke. So I decided to test the air quality inside my house. Turns out it was terrible! Almost as bad as outside. How did I test my air? Well, I am an air quality expert so I have lots of instrumentation to measure particulate matter, including several hand held units.

Smoke in Seattle, WA, August 2018

This got me thinking about what I could do about the air inside my house. It’s not a complicated problem, and there are several solutions that you can implement and they don’t cost much.

First, if you have air conditioning, most air conditioners have filtration and will remote smoke. Just make sure you change the filters regularly if it’s smoky out and use high quality air filters. More on this in a minute.

If you don’t have AC, but do have an air cleaner on your furnace, you can just run your furnace fans but with the heat off. I have an electronic air cleaner on my furnace and this should remove a large fraction of the smoke particles. Stupidly, I didn’t use it in 2018 when I discovered the bad air in my house! Now I know!

Lastly, you can build your own air filters for about $30–$50. These use basic 20” box fans on which you attach a high efficiency particle filter. A good video showing you how to do this is at the Puget Sound Clean Air Agency website.

Now about those filters….

Some people seem to think that any old filter will do. Many measurements show that wildfire smoke is in many ways like cigarette smoke. It is composed of many hundreds of different gaseous and aerosol particle compounds. Aerosols come in all shapes and sizes, but the important ones are those that are very small, less than about 2 micrometers (or microns) in diameter. These are the particles that get past our nose and deep into our lungs. We also know that wildfire smoke has thousands, millions, and even billions of very fine particles less than 1 micron in diameter. So we need a pretty darn good filter to keep this smoke out of our house.


The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) has developed a testing protocol for filters called Minimum Efficiency Reporting Values, or MERVs. This gives us info on the type of filter we need to use in our box fan to keep smoke out.

Less than a MERV 9 and you really aren’t much to keep smoke out. Filters rated MERV 9–12 are better and remove a significant amount of the 1–3 micron particles, but very little of the smaller particles. MERV 13 or 14 start to do a pretty good job of removing the most important smoke particles. There is one trade-off however. With these more efficient filters, one has to make sure the airflow is sufficient. If you are installing this on a box fan, there is no risk to using a MERV 13, and that is what I use at home and what is recommended by the Puget Sound Clean Air Agency. But if you are installing this on a home furnace system, airflow will be more important and it is best to consult with an expert on your heating/cooling system.

The question about why we are having so many fires is an interesting and important topic. Will these trends continue and we’ll have the same, or more, fires in the future? And how can you monitor the air quality in your own home? I’ll save these questions for a future blog post.

Does not have to be your real name
Your email will not be published
Newest Most Voted
Inline Feedbacks
View all comments
Rachel S.

This post has been helpful to many people, thank you! My friends and I have questions: – maybe for future blog posts?
* How can I tell the air quality Inside my home?
* What makes wildfire smoke dangerous? How does it compare to campfire smoke, or the smoke from bluegrass burning people used to do in the fall?
* What masks, if any, help with smoke inhalation?

Anjali G

Thank you as well. Any opinions on the idea of installing a Merv-13 in the window (well-taped all around) to bring in some filtered air & get some fresh oxygen?