Corsi-Rosenthal Boxes Help Clear the Air at Schools Across the Country

A book inspired a Virginia science teacher to make these DIY air filtration boxes, while colleges have embarked on large-scale projects to put Corsi-Rosenthal Boxes into public schools to slow COVID transmission and help with overall air quality.

High school environmental sciences teacher Carol Matheny didn’t want to start a new lesson the day before winter break, so she decided to give her students some reading time.

“Our librarians are phenomenal, and I told them I would really like to do a reading day,” says Matheny, who teaches ninth to 12th graders at Parkview High School in Sterling, VA. She couldn’t believe the number of books that arrived after her request.

The librarians curated 52 titles—including novels, graphic novels, and nonfiction—that related to subjects studied in Matheny’s classes, from evolution to invasive species and pandemics. As she looked to choose a book to model the reading she was asking of her students that day, a cover with a person in a plague mask persuaded her to pick up Deadly Companions: How Microbes Shaped Our History by Dorothy H. Crawford.

Matheny so enjoyed Crawford’s look at history, science, and pandemics, including SARS 2003, she took the book home to finish.

“It was a wonderful book, very inspiring,” says Matheny, who began thinking about what else she could do to help mitigate COVID-19 risks for herself and others. She was already following mitigation procedures as best she could, but knew there was more.

When a couple of snow days extended winter break, Matheny decided to attempt to make the Corsi-Rosenthal air-purifying box she had seen on social media.

“I think I’m a follower of every scientist on Twitter, and it caught my attention through someone I was following,” she says. “I saw this box, and I was intrigued. Then I started looking into it, and it looked really simple.”

Corsi-Rosenthal Boxes are effective, inexpensive, safe, and, by all accounts, easy to build. The DIY air cleaners were created by Richard Corsi, dean of engineering at the University of California (UC) Davis and Jim Rosenthal, CEO, Tex-Air Filters. The open-source design requires one box fan, four MERV 13 filters, and duct tape. Cardboard can help improve efficiency by acting as a fan shroud.

A study showed the boxes effectively reduce aerosols in indoor spaces. The aerosol transmission of the SARS-CoV-2, the virus that causes COVID-19, plus the increased transmissibility of the Omicron variant has put a spotlight on the need for proper ventilation and cleaning the air indoors as a key element to cutting down infections.

Matheny had two box fans that she had purchased to use when her classroom was too hot in the past. A large cardboard box from a recent purchase could be used for the base and as the fan shroud.

“I learned about fan shrouds,” she says with a laugh.

Matheny bought the filters at Home Depot and went home to get to work, with the help of video instructions. Before long, she had built two boxes and tweeted a picture of her creations in front of her Christmas tree with a shoutout to the librarians who introduced her to the book that helped inspire her.

She even received a response from Corsi himself, who offers a #CorsiRosenthal Box rater assessment of designs for those who tweet photos of their boxes with the hashtag.

“Well done, @cpmatheny17,” Corsi tweeted to Matheny. “Nice looking boxes. Well designed shroud. Bonus points for including students.”

When classes resumed, Matheny set up one of her boxes in her classroom “at breathing height” and another in a supply-closet-turned-staff-work-area that also has a copier in it. Bringing them to school gave her an opportunity to speak to students about aerosol transmission, the new variant, the purpose of the boxes, as well as share information about the box, its parts, construction, and function.

Matheny’s students are not the only ones sharing a space with a Corsi-Rosenthal Box. Across the country, concern about children getting COVID launched building projects and volunteer efforts that put them in classrooms from colleges to K–12.

At Brown University and UC San Diego, students built boxes for their classrooms and labs. Brown is also conducting a study on the effectiveness of the units.

One of the donated boxes in K.C. Boyd's library.
Photo courtesy K.C. Boyd

DC Public Schools librarian K.C. Boyd has three boxes donated by Peter Krupa, a parent in the district who started a GoFundMe campaign to raise money for the supplies. In less than a month, he was funded to build and deliver approximately 50 boxes.

By mid-January, a GoFundMe to build Corsi-Rosenthal Boxes for Winston-Salem/Forsyth County (NC) Schools district funded 66 units, put together by 40 volunteers.

Universities' public health efforts

Elsewhere, college faculty led the way and produced the boxes to bring better ventilation to local public schools.

A project by Arizona State University (ASU) placed 37 units as of mid-January with another 86 scheduled to be built, according to Megan Jehn, associate professor at ASU’s School of Human Evolution and Social Change. Jehn’s work involves COVID school outbreak investigation, which led her to the boxes project.

“We were just seeing such a high volume of cases in school settings, and so many outbreaks,” she says. “Here in Arizona, many schools were coming back without masking policies. So we thought that this might be one way for us to move the chain in terms of prevention. If I can't stop transmission in a classroom, maybe we can do something else to improve the quality of the indoor air that might sort of lower transmission.”

They started with the most vulnerable schools that had older buildings and communities at high risk because of intergenerational housing and other factors. At one point, she tweeted asking for teachers who might want one for their classroom.

“Then we just got overwhelmed with responses from teachers requesting boxes,” says Jehn. “We tried to do our best to prioritize based on high-risk settings, older school buildings.”

Across the country, Marina Creed, a faculty member at the University of Connecticut (UConn) School of Nursing and neuroimmunology nurse practitioner in the Multiple Sclerosis Center at UConn Health, worked with immunosuppressed patients concerned about getting sick and school as often the source of their fears. Parents worried about their kids bringing COVID home from school. Educators worried they would contract it at work.

“The schools were the weakest link in their ‘bubble’ as they were trying to keep themselves from getting infected,” says Creed.

So Creed did a little research, looking at the mitigation efforts in one district connected to a patient then broadening her research to the state’s policies.

“I took a look at what the COVID-19 return to school protocols were in the state of Connecticut, and I noticed that there were no portable air filters that were being used in the school systems, which is something that I saw was a public health recommendation by Johns Hopkins University and others,” she says. “So I started looking further into this as to what we can do to stack the odds in the favor of the children and the educators and the staff in the schools to minimize the risk of contracting COVID-19 and minimize transmission. That's when I found the idea of [the] Corsi-Rosenthal Box.

"I thought that it was a brilliant way to have a multi-layered mitigation strategy to prevent transmission of COVID-19, or at least to reduce the risk. So our team at the University of Connecticut started studying the boxes and looking to implement them into schools.”

The Corsi-Rosenthal Box public health initiative that developed from Creed’s initial research includes the health center and the Schools of Nursing, Engineering, and Medicine.

Angela Starkweather, a professor and associate dean for academic affairs at the UConn School of Nursing, saw an opportunity not only for faculty and staff, but also students. She brought students into the process to go into the community and teach people how to build the units, as well as educate them on why filtration systems are an important part of mitigation strategies.

As of mid-January, the UConn team had deployed 100 units to West Hartford Public Schools. As part of a second-semester class, students in the School of Engineering are building 200 more air cleaners to give to Coventry Public Schools, and the school of medicine is building another 100 for the Hartford community, including approaching school systems. The engineering students will also run tests on their air cleaners and analyze the data as part of their academic work. 

Jehn’s group is not testing air quality in buildings with the boxes. Measuring air quality was a point of resistance from schools that appeared afraid they would look bad if their air was revealed to be unhealthy.  Jehn is in discussion to get cooperation from some schools to study the impact of the boxes, she says, and hopes to partner with the UConn team and share protocols for field testing.

“We would love to find a way to make this sustainable, to help the school sort of make this part of their regular fall check-in process—update the filters, update the box, and keep it going,” says Jehn, who is hoping for funding for ongoing research projects and to develop lesson plans and make it part of the STEM curriculum to teach students about public health and disease transmission.

“I see a lot of potential for this to continue,” she says.

As a final part of its project, the UConn group is creating a website to host all of the information for schools to build these themselves. Creed hopes this work gets picked up by other colleges.

“I am hoping to help other universities and states grow this movement to deploy DIY air filters into public schools, especially as a STEM project for classrooms, as improved indoor air quality in K–12 schools is a long-standing need of our communities,” Creed says.

The Corsi-Rosenthal Boxes are great STEM or makerspace projects with value beyond the current pandemic. They can filter dust, pollen, viruses, and other pollutants from the air in classrooms. In California, they have been used to mitigate wildfire smoke indoors. The boxes can be too big for some spaces, so after receiving requests, Rosenthal created a mini version.

Even with the federal COVID-19 recovery funding, districts with old school buildings or that have been historically underfunded often can’t renovate the HVAC system or afford portable HEPA filters for every classroom. Instead, parents, educators, and local volunteers are building and donating units to combat the coronavirus. Many hope to continue past the pandemic, when the units will mean better overall air quality and, in turn, a better learning environment.

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Kara Yorio

Kara Yorio (, @karayorio) is senior news editor at School Library Journal.

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