This $30 box can save your lungs during wildfire season

A cardboard box with four HVAC filters and standard fans may be your best defense against wildfire smoke and respiratory particles, according to a study yesterday at the American Chemical Society Spring 2025 Digital Conference.

DIY air cleaners (called Corsi-Rosenthal boxes) cost a small portion of commercial HEPA filters, but may outweigh their performance in removing harmful particles from indoor air.

“The media didn’t focus much on indoor air quality, and then the pandemic broke out and suddenly there was a huge opportunity to educate the public,” said Richard Corsi, dean of the University of California’s Davis School of Engineering.

Although Americans spend about 90% of the time inside, research on indoor air quality focuses less on outdoor pollution than on outdoor pollution. This balance changed during the 19th pandemic, just as wildfire seasons grew longer and more intensely in most parts of North America.

CORSI and filtration expert Jim Rosenthal jointly designed the system to help people who can’t afford expensive air purifiers. The simple device consists of four standard HVAC filters arranged in a cube, a cardboard base and a box fan that pulls air into the filter and guides it to the ceiling.

“That’s the idea of ​​us coming up with a low-cost, effective air cleaner,” Cosey explained.

Better than expensive alternatives

The UC Davis team tested the DIY filter by installing units on campus and running for 2500 hours, equivalent to two K-12 academic years. The results are surprising.

Homemade units not only match commercial HEPA purifiers, but sometimes outperform them, especially particles between 1-3 microns in diameter, which ranges include common allergens and certain dust particles.

Although the HEPA filters are more technically effective in capturing particles in a single pass, the overall air of the Corsi-Rosenthal box is larger, resulting in more particles being removed from the indoor environment. Even after extended use, DIY systems are still competitive with more expensive alternatives.

Beyond smoke and dust

The researchers also explored whether these simple boxes could help reduce the spread of the disease by filtering respiratory particles.

In a simulation of two people talking on the table, the DIY filter quickly dissipates the breathing feather when placed within 3-4 feet of the conversation. This suggests potential applications to reduce the spread of air diseases in schools, offices and homes.

“We established a situation where two people talked about the breathing plume simulator across the table,” Cosey said. “We then measured the attenuation of the plume without the CR box and had the boxes around the room and ran at different speeds.”

The experiment showed that when the properly positioned filter was operating nearby, the respiratory particles dispersed within a few seconds.

Future improvements

Looking ahead, Corsi envisions several enhancements to the design. He hopes to develop quiet fan blades and modify filters to capture additional indoor contaminants from ozone from furniture and office equipment, such as formaldehyde.

In addition to technical success, Corsi is also satisfied with how the project empowers people to control the indoor environment.

“One of the things that satisfy me is telling me they know they are building things that help them, their families or their students, so they get such excellent personal satisfaction.”

As wildfire season approaches in many areas, this budget-friendly air filtration method provides practical solutions for homes, schools and workplaces, involving indoor air quality but is limited by limited resources.

The study was funded by the University of California, Davis.