By Allison Bailes III, Ph.D. —

The DIY box fan air cleaner known as the Corsi-Rosenthal Box (or the Comparetto Cube, in a slight variation) has really taken off in the fight against COVID.  I wrote about it here in September 2020, with instructions on how to make one yourself after I made my first one.  I just changed the filters on mine yesterday, so it’s a good time for a little update on this clever device.

Does it work?

I guess it shouldn’t surprise me anymore, but I’ve seen some people claiming it won’t work or won’t last long or it works but it won’t help with COVID.  So, here’s a quick review.

1. Particulate matter in the 2.5 micron and smaller range is the worst for human health overall.
2. Particles carrying active viruses, like the SARS-COV-2 responsible for COVID-19, come in a lot of different sizes.
3. The small particles that stay airborne for hours are responsible for a lot of the COVID infections.  (Unfortunately, the CDC and WHO have been slow to recognize this and promote the obvious solutions.)
4. Filters remove particles from the air.
5. High-efficiency filters remove more particles and smaller particles.  MERV-13 is where you want to be.
6. Taping one MERV-13 filter works, but the high resistance reduces its effectiveness.  It also needs to be replaced sooner than the Corsi-Rosenthal Box or Comparetto Cube configurations.
7. Two filters is better than one because of the reduced resistance.
8. Four or five filters is best.  It has great air flow, as measured by John Semmelhack and Neil Comparetto.  (See chart below.)  That means it has a great Clean Air Delivery Rate (CADR) when you use MERV-13 filters.

Read the full article in the Jan-Feb issue of Healthy Indoors Magazine at: https://hi.healthyindoors.com/i/1455789-hi-jan-feb-2022-usa-edition/33