DIY Air Filter Found 99% Effective

Sign up for the Morning Brief email newsletter to get weekday updates from The Weather Channel and our meteorologists.

A do-it-yourself air filter that went viral during the Covid-19 pandemic actually works.

It works so well, in fact, that a new study by the U.S. Environmental Protection Agency found that it’s 99.4% effective at removing infectious particles from the air over the course of an hour.

“These CR boxes really work. The Corsi-Rosenthal box works against infectious aerosols in the air. The results are really powerful.” EPA scientist Katherine Ratliff, who led the study, said in a news release.

The so-called Corsi-Rosenthal box can be made at home fairly easily for under $100 and with zero tools.

Here’s how to build one:

First, you’ll need the following items that can be found at a local hardware store:

-A box fan, like this one from Lasko.

-Four MERV 13 air filters, like these from Home Depot.

-A roll of duct tape (you’ll use a lot, so make sure you have enough on hand or buy a fresh roll).

-Two sheets of cardboard are optional for the base and top.

Step 1:

Assemble the outside of the box with the air flow oriented so that it’s facing inside the box. Duct tape the edges and around the top and bottom of the air filters so you have a secure, sturdy box that stands on its own.

Step 2:

Attach the box fan to the top of the air filters with the fan’s power facing up. Add another layer of duct tape to attach the fan, making sure that no air escapes through the sides.

Step 3 (optional):

Cut cardboard into a square for the base, and cut out a circular hole that is about as wide as the fan blades. Tape to the top and bottom.

Here’s a handy printable guide from the University of California, Davis.

Senior producer Niki Budnick writes about breaking weather news, pets, lifestyle, health & wellness and more for weather.com.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.