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Making Spaces Safer

An easy-to-build box can help in the fight against COVID-19.

Diagram of four filters and a box fan fitting together alongside an illustration of a completed Corsi-Rosenthal box (CC BY 2.0)

A simple device that just about anyone can put together is proving to be a valuable tool in the fight against COVID-19. The Corsi-Rosenthal box is a build-it-yourself air filter that has been shown to reduce the number of virus particles in indoor settings. 

Scientists say air filtration is an important part of protecting people from COVID-19. That’s because the virus that causes COVID-19 can remain in the air for hours, even after an infected person leaves the area. Invented by engineer Dr. Richard Corsi and Jim Rosenthal, the head of an air filter company, the Corsi-Rosenthal box is a fairly inexpensive alternative to store-bought air-cleaning devices. Scientists at 3M, a company that makes air filters, tested the Corsi-Rosenthal box and found it was effective at capturing virus particles.

The ingredients for a Corsi-Rosenthal box are available at most hardware stores. They include a box fan, four or five high-quality furnace filters, some cardboard, and duct tape. Building instructions can be found on many websites. Assembling the device is as simple as putting flat objects together to form a cube.

Because they’re so easy to make, the boxes have become increasingly popular. Many people have built them for their homes and workplaces. Volunteers have also built boxes for schools and homeless shelters.

Experts caution that air cleaners alone are not enough to make indoor spaces safe. But, along with ventilation, vaccination, and mask-wearing, these portable devices can make a big difference.

In the fight against COVID-19, every weapon counts.

How to Build a Corsi-Rosenthal Box

 You will need:

  • Four MERV13 furnace filters
  • One box fan
  • Duct tape
  • A large piece of thick cardboard


  1. Duct tape four MERV 13 furnace filters so you form the sides of a cube. Make sure the filters are facing the right way. The air flow should go into the cube.
  1. Cut a piece of thick cardboard that is the same size as the filters. Duct tape this cardboard so it covers one of the open sides of the cube. This is the side of the box that will sit on the ground.
  1. There should be one remaining open side of the cube, at the top. This is where your box fan will go.
  1. Duct tape the box fan to this open side of the cube. Make sure the fan is facing the right way. The air from the fan should blow out of (not into) the cube.

Did You Know?

Sign from 1918 that reads Keep your bedroom windows open! Prevent influenza-pneumonia-tu

National Archives, College Park, MD (ARC Identifier: 45499333)

Scientists have learned a lot about viruses since 1918, when an influenza pandemic swept across the globe. But even 104 years ago, scientists understood that clean indoor air was important.

Stepping Up

Teenage boy standing next to a Corsi-Rosenthal box

Courtesy of Kavita Taneja

A Canadian teenager named Shiven Taneja has built more than 60 Corsi-Rosenthal boxes for neighbors and local senior citizens. He built the first one for his grandparents and then decided he wanted to help others in need. 

Taneja decided to step up because he realized that it might be difficult for some people to do the physical work of building the boxes. Although the boxes are simple, putting them together requires a lot of bending and stretching.

It takes Taneja less than two hours to build one box. He charges about 119 U.S. dollars for each one. That’s just the cost of the materials, and it’s a lot less than the cost of a store-bought air filter.“ Not everyone can afford a [store-bought] filter,” Taneja told the Toronto Star. “[I realized] I can step up; I can do this.”

The Young Inventor

Sometimes solving problems means thinking outside the box. When he was a teenager, William Kamkwamba built a windmill so that his village would have electricity.

Taylor Jewell/Invision—AP/




: skill or cleverness that allows someone to solve problems, invent things, etc.

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