Super cheap DIY air filter to deal with the wildfire smoke.

Michael E Johnson
3 min readJun 28, 2023

Smoke from the Canadian wildfires has gotten really bad this year. Luckily, there’s a cheap and readily available way to filter the air in your house.

airnow.gov reported air quality in our area has been getting pretty bad, heading above 260 for PM2.5

Pandemic Research to the Rescue

During the pandemic, Engineers Richard Corsi and Jim Rosenthal created a filter design based on cheap 20 inch box fans and common HEPA household air filters to remove virus particles from public spaces. Their design (show ) is excellent, and allows for processing massive amounts of air in public spaces using four air filters. Their design was released to the public to improve health in public spaces like schools that might not have the air flow and filtering to handle pandemic viral loads. The design takes up a lot of space, however.

The original Corsi–Rosenthal Box ( Wikipedia )

We built such a box for home use, and noticed a great improvement in everyone’s allergy symptoms. When the filter began to fill up, we went down to a single filter version (pictured), which worked very well and only required changing once every couple of months. It also takes up much less space. Build instructions are listed below.

DIY Corsi-Rosenthal single panel filter:

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Michael E Johnson

Inventor building an iron-based battery for the one billion humans living without access to light once the sun goes down. www.bigattichouse.com