This DIY Air Purifier Costs Much Less Than a HEPA Purifier, and Studies Show It Works

TORONTO — This fall, teachers and parents shared photos on social media of DIY air purifiers they made for classrooms to protect children from transmitting COVID-19. 19.

But do these cheap purifiers really work?

According to the researchers, yes.

They are called Corsi-Rosenthal Boxes, a DIY air purifier that was first designed in the summer of 2020 by two air filtration experts, Richard Corsi and Jim Rosenthal.

Since then, their effectiveness has been confirmed by scientists, studies and a company that manufactures air filters.

Studies have shown that poor ventilation is associated with much higher spread of COVID-19. But many buildings in Canada, including schools and workplaces, are still not equipped with proper ventilation systems or HEPA purifiers.

Unlike HEPA purifiers, which can cost anywhere from $200 to over $500, a Corsi-Rosenthal box can be made for around $100 with materials that can be purchased at any hardware store.

A York University engineering professor who carried his Corsi-Rosenthal box with him to campus last week says he heard about it on social media in mid-2021.

“Some ventilation engineers were talking about it and it seemed like a convenient and easy way to get more clean air into schools and into my home,” James Andrew Smith told in an email.

“I don’t think we’re doing enough for clean air,” he added, saying he felt better about the level of risk in his class when using the DIY air purifier with other measures.

The boxes also seem to have longevity.

“That guy behind me just turned eight months a few days ago,” Corsi said in a video on Twitter on Monday, referring to his own Corsi-Rosenthal box buzzing behind his shoulder. “Still does its job, still reducing inhalation dosed aerosol particles, including virus-laden respiratory aerosol particles. It’s not rocket science, friends.


There are variations, but the basic Corsi-Rosenthal box is made up of four air filters, a box fan, and cardboard, all glued together to form a cube. A tutorial from the University of California at Davis specifies using MERV-13 filters.

The box fan should have the airflow directed outward and all edges should be sealed with tape. The last sixth side of the cube should be closed with cardboard or even a fifth air filter.

To make the filter more effective, you can also cut a circle out of a piece of cardboard and tape it to the outside face of the box fan to reduce backdraft.

The idea behind the Corsi-Rosenthal setup is that air entering the box will pass through multiple filters for purification, and the sealed cube means that only filtered air will then be blown into the room by the fan.

Studies indicate that while it won’t be able to filter out as many particles as a HEPA filter, a Corsi-Rosenthal box can circulate the air in a room at a rate that sometimes exceeds HEPA purifiers, eliminating virus particles from the air. at a fraction of the cost.

A study published in March in the journal Aerosol Science and Technology, which included Corsi as one of its authors, found that the canisters were able to quickly filter an entire room at a much faster rate than HEPA purifiers.

Looking at the “cost per air cleaning unit”, the study states that “the DIY air filter is about one-tenth the initial cost of a commercially available HEPA-based air purifier” .

3M, a company that makes air filters, said in a February press release that its scientists had studied Corsi-Rosenthal boxes and the DIY idea worked.

“Indoor air is shared air,” Kelsey Hei, 3M Filtrete brand engineer, said in the release. “Many viruses like COVID-19 are airborne and can become highly concentrated in poorly ventilated spaces. I am heartened to see so many people championing the importance of clean air, especially in schools.

Another study published in September in the journal Science of the Total Environment looked at nine different configurations of DIY air purifiers and compared them to three HEPA purifiers.

The study found that DIY options, including a single filter with a box fan, Corsi-Rosenthal boxes, and a variant of these that uses three filters and two box fans in a cube, were all comparable or better than HEPA purifiers in terms of how fast they filtered the air.


When it became clear that COVID-19 was being spread through the air, scientists began to emphasize the importance of good ventilation as a tool to slow transmission.

An Italian study published last March and involving more than 10,000 classrooms found that effective ventilation systems were able to reduce the transmission of COVID-19 in schools by more than 80%.

Infections were much lower in the 316 classrooms equipped with a mechanical ventilation system, compared to those without. When ventilation systems completely replaced classroom air with fresh air 2.4 times per hour, infections were reduced by 40%. If they replaced the air six times an hour, infections were reduced by 82%, according to the study.

With few public health measures still in place for back to school, teachers are increasingly turning to tools like the Corsi-Rosenthal Box to make their classrooms safer.


As students returned to class this fall, teachers and parents took to social media to share photos of their Corsi-Rosenthal boxes. On Twitter, the hashtag #CorsiRosenthalBox includes many creative designs intended to be child-friendly.

A Manitoba-based user posted a photo of a Corsi-Rosenthal box for his son’s classroom that had been upgraded to look like a robot, complete with googly eyes, antennae and arms.

Other designs used large eyes, brightly colored paint, and a variety of animal ears to transform boxes into friendly creatures.

In Quebec, parents and teachers have posted a petition asking Jean-François Roberge, Minister of Education, to allow them to provide Corsi-Rosenthal boxes to their children’s schools, saying that citizens’ initiatives have “run up against a strong administrative resistance.

“Installing homemade air purifiers, known as Corsi-Rosenthal cubes, is an effective and inexpensive way to improve air quality in indoor spaces,” the description reads.

The petition, launched last month, has more than 1,600 signatures.

At York’s Lassonde School of Engineering, Smith says carrying around a Corsi Rosenthal box sparked questions and curiosity from students.

“How much do I care about my students? Enough to build them a wheeled #CorsiRosenthalBox to bring to class,” he tweeted on Monday.

Smith and other faculty members have petitioned the dean’s office at York’s Lassonde School of Engineering to fund and distribute portable air purifiers to faculty members, but so far those requests have been met. rejected.

“I personally think they’re a no-brainer,” Smith told “They’re easy to set up, easy to use, aren’t pretty much the controversial topics that vaccines or masks are. They clear the air for smog, smoke, dust…they are usually a great idea.

These boxes are used in classrooms all over the world.

In November 2021, Brown University School of Public Health in Rhode Island began a project to build Corsi-Rosenthal boxes for classrooms and study them, and has since installed boxes in many classrooms and student lounges. .

UK county councilor Oliver Patrick launched a GoFundMe last month to provide Corsi-Rosenthal boxes to schools in his district, saying he was concerned about the lack of public health measures in place in his area .

“I want to make sure we are doing everything we can to make school as safe as possible for the kids,” Patrick wrote.

The California Department of Public Health listed Corsi-Rosenthal boxes as a recommended option for classrooms in a February bulletin to improve air quality in schools to combat COVID-19.

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