Build a Corsi-Rosenthal filtration box for COVID-19

Home-built indoor air ventilation and filtration system

Since COVID is airborne and the Omicron variant extremely contageous, indoor air quality has never been more important. At the Italian school of San Diego, all classroom have very good ventilation thanks to having a door facing outside and a door facing the auditorium. Except one that has both doors facing the auditorium, so we felt the necessity to supplement ventilation in that room using a Corsi-Rosenthal box.

In this post I’ll share some images on how to build a Corsi-Rosenthal filtration box, here is the final product:

Shopping list

• 5 MERV 13 filter, 2 inch thick from Tex-Air filter, $79 with shipping, alternatively you can find filters at Home Depot, Costco or Target, but they are 1-inch thick. I received them in less than 1 week.
• 20 inch box fan, $32 on Amazon
• Gaffer tape (seals better than duct tape), white, $19 on Amazon

Building process

There are several online videos, I followed this one on Youtube, and the blog post by Jim Rosenthal.

A few photos of the process, I also cut a small slit in the back of the fan for the power chord to improve contact with the filters.

Fan shroud

Finally I added a fan shroud to improve efficiency, as suggested by David Elfstrom, the internal diameter of the shroud should be 13.5 inches with a Hurricane fan.