34 | January/February 2022
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.
The fan is round, but the housing is
square. At the corners, some of the air
will be going the other direction. To im-
prove air flow and eliminate that bypass,
you can make a shroud out of cardboard
to cover the corners. That's what I did
differently when I changed the filters on
mine yesterday. See the photo at the top
of the article. Jim Rosenthal has an article
all about the box fan air cleaner shroud.
Creativity Abounds
Just today I found another variation on
the DIY box fan air cleaner. The photo
below is from Canada Strong Masks and
uses two filters that are larger than the
standard 20" x 20" filters used in the 4 or
5 filter versions. In a tweet, they say they
place them 7 feet off the floor and blow-
ing the air upward to reduce noise.
and offices. Parents and teachers have had
their students make them as class projects.
It's been the subject of quite a few news
stories.
It even got the Idea of the Year Award
from the Waterloo Filtration Institute.
There's also a Wikipedia page for the
Corsi-Rosenthal Box, which I discovered
just today as I was researching for this
article. And Ask This Old House covered it
in a show, too.
This is all great! We need more of
these things.
Improve Filtration
When I made my first Comparetto Cube
in 2020, I copied the design I had seen
online. But that early design isn't fully
optimized because there's some bypass
at the fan. The photo below shows a red
circle highlighting the area through which
the fan moves the air.
The DIY box fan air cleaner has some bypass at
the corners of the box fan.
If you haven't made your own DIY
box fan air cleaner yet, why not? It looks
like we're stuck with COVID for a while
longer. But even when COVID is gone,
these devices are great for improving
your indoor air quality. And they're
especially great for those of you who live
in places that get smokey from wildfires.
Related Articles
How to Make a High-MERV DIY Portable
Air Cleaner
COVID Is Airborne — Are You Feeling Lucky?
3 Ways to Get Cleaner Indoor Air With
Filtration
IAQ Research-Practice in Action: The
Corsi/Rosenthal Box Air Cleaner by Jim
Rosenthal of TexAir Filters
Allison Bailes
Allison Bailes III,PhD is a speaker, writer, building science consul-
tant, and founder of Energy Vanguard in Decatur, Georgia. He is
also writing a book on building science. You can follow him on
Twitter at @EnergyVanguard.
Two filter variation of the DIY box fan air cleaner.
May's Ways
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