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air quality section (AQS)

The Corsi-Rosenthal Box: A "Do-it-Yourself" Portable Air Cleaner

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[1] 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.

The box is a do-it-yourself portable air cleaner
Source: cc

Construction: How to Build It

​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.

Construction of box includes box fan, 4 MERV-13 filters, and cardboard
Source: cc

Instructions for use

  • Don't leave children unattended when the fan is in use
  • Set at the highest fan speed acceptable for the noise level
  • Do not place directly against a wall, under a table, or near an open window
  • Take care that the power cord doesn't create a tripping hazard
  • Replace the filters at least every 6 months, or more frequently during wildfire season


[1] High-Efficiency Particulate Air [filter]

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