The Current

Meet the Ontario teen building DIY air purifiers for seniors and small businesses

Shiven Taneja, 14, is building DIY air purifiers for people in his Mississauga, Ont., neighbourhood. He's so far built around 20 of the boxes, called Corsi-Rosenthal boxes, since starting the project in mid-December.

'I wanted to do my part, despite just being 14,' says Shiven Taneja

Shiven Taneja, 14, stands in front of some of the Corsi-Rosenthal boxes he built. (Submitted by Kavita Taneja)

At just 14, Shiven Taneja didn't spend his Christmas break like many of his classmates, occupied by video games, bingeing Netflix or even relaxing after a long semester of schoolwork. 

Instead, as the country saw COVID-19 numbers surge once again, driven by the Omicron variant, the teen rolled up his sleeves and started building homemade air purifiers for those in his community of Mississauga, Ont.

"Anxiety levels were rising again, and over my winter break, I had the time. So I felt like, why not just do it?" he said in an interview with The Current's Matt Galloway.

Known as Corsi-Rosenthal boxes, the do-it-yourself devices were developed in 2020 by two air filtration experts, Dr. Richard Corsi and Jim Rosenthal. (Although some experts credit Kris Ray, the air quality program manager for the Confederated Tribes of the Colville Reservation in Washington state, for developing similar units as early as 2019.)

On Boxing Day, Taneja posted an offer on Twitter to build the boxes for others. That post went viral and Taneja has since built around 20 of these devices for neighbours, local seniors and even a fencing studio.

Since building his first Corsi-Rosenthal box on Dec. 12, Taneja has built around 19 more units. Some of his customers include neighbours and an Oakville, Ont.-based fencing studio. (Submitted by Kavita Taneja)

Initially, he was only going to build a unit for his family. But he soon figured others in his community could also benefit, particularly seniors.

"I decided, well, getting the materials [and] actually building it might be hard for elderly people, so I decided I would build it for them," he said.

He charges $150 for each unit, which is just the cost of the materials. It usually takes Taneja an hour or two to build one, but he said the process is "surprisingly easy." 

"The older you are, the harder it is — because you have to continuously bend down and sit," he said. "But for me, it's around two or three on a scale of 10."

Taneja says he's always had an interest in engineering; he's previously tinkered with Popsicle sticks, motors and 3D printers. While these air purifiers were his first large-scale build, that wasn't enough to deter him.

"I wanted to do my part, despite just being 14."

Bang for the buck

The Corsi-Rosenthal boxes that Taneja builds consist of four 3M 1900 grade air filters and a 20-inch box fan. Taneja carefully tapes the filters together to form a box shape, and then tapes the box fan on top.

"The fan is blowing up and sucking air through the filters," he said. "As the air is pulled through the filters, it removes any particles [that could be] carrying the virus."

It's unclear how many coronavirus particles are filtered out by these boxes — if any at all. But a case study done by researchers at the University of California, Davis's Western Cooling Efficiency Center suggests they could be helpful.

WATCH | Shiven Taneja walks us through building a Corsi-Rosenthal box:

Shiven Taneja explains the Corsi-Rosenthal box

5 months ago
Duration 1:23
14-year-old Shiven Taneja is building DIY air purifiers for people in his neighbourhood. He's built around 20 of these boxes, called Corsi-Rosenthal boxes, since Dec. 12, 2021. He walks The Current through the materials he uses to build the units.

While Corsi-Rosenthal boxes might look quite simple, there's a lot to like about the devices, says Jeffrey Siegel, an engineering professor at the University of Toronto and a leading expert on ventilation.

"The reason there are four filters in a box is that gives you a lot of surface area — and that helps with the pressure drop," said Siegel. "So that fan is able to move more air than it could when it's just the single filter."

That's a key part in determining the Clean Air Delivery Rate (CADR) of an air purifier, which indicates how effective the device is at removing contaminants — such as dust, pollen and smoke — from the air. A CADR is usually listed in either cubic feet per minute (cfm), or in Canada, in cubic metres per hour (m3/hour). 

"[CADR] gets at the efficiency piece and the flow-rate piece," said Siegel. "So a good air purifier — forgetting all of the other details — is one that has a high CADR."

Assuming the filters and the fan he's using are all of good quality, Siegel estimates that the CADR of Taneja's average build lies somewhere between 300-350 m3/hour.

As a rule of thumb, Siegel said a filter for a small room should have a CADR between 200 and 250 m3/hour, while a bigger room should have a CADR between 400 and 500 m3/hour. 

"The DIY air cleaner is a good example of why having those four filters is important," he said. "The fan is able to move more air, because it's seeing a lower pressure drop, because the filter is distributed over a larger area."

WATCH | Jeffrey Siegel explains how to keep your home's air clean without a store-bought air purifier:

How to clean the air in your home without spending hundreds of dollars

1 year ago
Duration 4:00
An indoor air scientist explains what you can do to keep your home’s air clean without buying a purifier.

But Siegel also noted that Corsi-Rosenthal boxes aren't perfect; aside from the quality of the original materials, which are often purchased cheap, replacing those taped-together filters could pose a problem down the line, he said.

"You've got to go find the filters at the hardware store, you've got to tape them yourself, [and] if you don't tape them well, you're probably going to get a less well-performing air purifier," he said.

But given what a consumer could otherwise get for $150, which is far less than most store-bought brands, Siegel said there is some benefit to investing in a Corsi-Rosenthal box.

"Especially if you were to look at a metric like CADR per dollar, it's going to look fantastic compared to any commercial air purifier," he said. 

Knowing that something I created can help someone, it's a really good feeling.-Shiven Taneja

Helping the community

And that's exactly why Taneja decided to pursue building his own DIY air purifiers in the first place — both for himself and his neighbours.

Still, he said he didn't expect the reaction he received when he first tweeted about his build.

"I expected, like, a few people at most to order. And maybe 100 likes at most," he said. "I could never imagine having this many likes and getting retweeted this many times."

But for Taneja, it's not the numbers that matter most — it's the reception he's received from people who've ordered a box, showing they believe in him and what he's doing.

"It feels really good, especially when I deliver a box," he said. "Knowing that something I created can help someone, it's a really good feeling."

This individual stepped up to do their part, why aren't we all stepping up to do our part?-Jeffrey Siegel

Siegel said he'd like to see more people share Taneja's community spirit.

"It's criminal that there's not a truckload of filters sitting outside [his] house now … that someone isn't stepping up and providing fans, and that someone else isn't thinking about this question of distribution," he said.

"This individual stepped up to do their part; why aren't we all stepping up to do our part?"

Written by Mouhamad Rachini. Produced by Ben Jamieson and Liz Hoath.

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