The Corsi-Rosenthal box is a do-it-yourself (DIY) portable air cleaner that can improve air quality indoors. You can use them to reduce the spread of infectious diseases like COVID-19, smoke from wildfires, and other particles that get in the air like dust and pollen.
Preliminary tests are finding Corsi-Rosenthal boxes to be an effective and cheaper alternative to commercial HEPA based portable air cleaners. If you build a DIY air cleaner, buy a new fan with a UL or ETL safety marking to avoid fire risk.
Corsi-Rosenthal boxes are constructed from a box fan, four MERV-13 filters, and cardboard. Choose a fan with the speed dial on the side, not the back. A cheaper single-filter design can also be used in smaller rooms, although it will not be as effective as the 4-filter design.
The corners of the fan should be covered with a cardboard "shroud" or duct tape to improve airflow.
In-depth video instructions to build a Corsi-Rosenthal box can be found from the University of California, Davis: UC Davis How to build Corsi-Rosenthal Box.
Instructions for use