Richard Corsi demonstrates the airflow of a low-cost, DIY air cleaner that can remove indoor pollutants such as smoke particles and respiratory particles. It may also reduce the spread of airborne viruses.
Richard Corsi demonstrates the airflow of a low-cost, DIY air cleaner that can remove indoor pollutants such as smoke particles and respiratory particles. It may also reduce the spread of airborne viruses.
A cardboard box with four HVAC filters and a standard fan could be your best defense against wildfire smoke and respiratory particles this summer, according to research presented yesterday at the American Chemical Society’s Spring 2025 Digital Meeting.
The DIY air cleaner, known as the Corsi-Rosenthal Box, costs a fraction of commercial HEPA filters yet matches or exceeds their performance in removing harmful particles from indoor air.
“The media didn’t pay much attention to indoor air quality, and then the pandemic hit and suddenly there was this tremendous opportunity to educate the public about the issue,” said Richard Corsi, dean of the University of California, Davis College of Engineering, who presented the findings.
Indoor air quality has historically received less research attention than outdoor pollution, despite the fact that Americans spend roughly 90% of their time inside. That balance shifted during the COVID-19 pandemic, just as wildfire seasons were growing longer and more intense across much of North America.
Corsi and filtration specialist Jim Rosenthal co-designed the system to help people who couldn’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 through the filters and directs it toward the ceiling.
“That’s when we came up with the idea of a low-cost, effective air cleaner that people can build themselves,” Corsi explained.
Outperforming Expensive Alternatives
The UC Davis team put the DIY filters to the test by installing units across campus and running them for 2,500 hours – equivalent to two K-12 school years. The results were surprising.
The homemade units not only matched commercial HEPA purifiers but sometimes outperformed them, particularly for particles between 1-3 micrometers in diameter – a range that includes common allergens like pollen and some dust particles.
While HEPA filters are technically more efficient at trapping particles in a single pass, the Corsi-Rosenthal Boxes process more air overall, resulting in more particles being removed from indoor environments. Even after extended use, the DIY systems remained competitive with more expensive alternatives.
Beyond Smoke and Dust
The researchers also explored whether these simple boxes could help reduce disease transmission by filtering respiratory particles.
In simulations where two people spoke across a table, the DIY filter rapidly dissipated respiratory plumes when placed within 3-4 feet of the conversation. This suggests potential applications for reducing airborne disease transmission in schools, offices, and homes.
“We set up a situation where two people are speaking across the table next to a respiratory plume simulator,” Corsi said. “We then measured the decay of that plume with no CR Box and with boxes located around the room and running at different speeds.”
The experiment showed respiratory particles dispersed within seconds when a properly positioned filter was operating nearby.
Future Improvements
Looking ahead, Corsi envisions several enhancements to the design. He hopes to develop quieter fan blades and modify the filters to capture additional indoor pollutants like formaldehyde from furniture and ozone from office equipment.
Beyond the technical success, Corsi finds satisfaction in how the project has empowered people to take control of their indoor environments.
“One thing that’s been so satisfying to me is the number of people who’ve told me that they get such great personal satisfaction out of knowing that they’re building something that’s helping them and their families or their students,” he noted.
As wildfire season approaches in many regions, this budget-friendly approach to air filtration offers a practical solution for households, schools, and workplaces concerned about indoor air quality but constrained by limited resources.
The research was funded by UC Davis.
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