this post was submitted on 08 Jul 2025
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Mildly Interesting

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I recently stayed in an apartment that didnt have central air so I created a corsi-rosenthal box since the smoke from the Canadian wildfires were so bad.

After 30 days of continuous use, with very minimal periods of it being turned off, this is what the filters look like!

It's disgusting yet also so satisfying to see the filters get darker from debris, dust, and dirt.

Edit: typos

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[–] [email protected] 98 points 3 days ago (19 children)

"Corsi-Rosenthal Box" sounds like it's some theoretical physics thought experiment, but no it's some filters and a box fan.

Be tempted to build one of those for my shop.

[–] [email protected] 15 points 3 days ago* (last edited 3 days ago) (2 children)

I thought it was for filtering weed smoke, designed by the famous grower and strain creator Ed Rosenthal.

[–] [email protected] 2 points 3 days ago (1 children)

That a good idea ! Didn't think about it.

[–] [email protected] 8 points 3 days ago (1 children)

well..

A 2022 study found the clean air delivery rate on the five-filter design was between 600 and 850 cubic feet (17–24 m3) per minute (depending on fan speed), costing roughly a tenth of commercial air filters.

hope you can keep up!

[–] [email protected] 1 points 3 days ago

Yeah may be a little overkill

[–] [email protected] 13 points 3 days ago (2 children)

Think it was a covid thing.

No word on ed being the rosenthal in question.

[–] [email protected] 10 points 3 days ago (1 children)

These have been around for a long time as DIY filters for folks, I remember seeing one of these on Reddit before comments were a thing.

Once upon a time Reddit drove you to interact with other websites instead of shitposting your best hot take about the title of the post someone else didn’t even visit.

Comments truly ruined Reddit

[–] [email protected] 4 points 3 days ago (1 children)

Long time ago I made my own activated carbon filter from plans I found online out of chicken wire, some duct parts, of course activated carbon, and pantyhose. got some funny looks when buying that last one, but it worked like a freaking charm.

[–] [email protected] 3 points 3 days ago

custom filters are common in the aquarium hobby, lots of fun pipe fittings to play with

[–] [email protected] 15 points 3 days ago (2 children)

Someone posted a link to Wikipedia in the comments, came across their names:

Richard Corsi, an environmental engineer and the incoming Dean of Engineering at the University of California, Davis

Jim Rosenthal, the CEO of filter manufacturer Tex-Air Filters

[–] [email protected] -1 points 3 days ago (1 children)

Oh. A CEO of a filter company. I sort of wondered why I couldn't just tape a single filter to a fan, why it required four of them. Maybe it has something to do with air flow limitations, or maybe it has something to do with the guy making a profit on every filter sold lol

[–] [email protected] 1 points 2 days ago (1 children)

Pretty sure its about creating negative suction below the fan. Instead of just pulling air from the intake side of the fan, its pulling it from all 4 directions. Theoretically the air flow going through the filter would be at least 4x but probably more in practice.

[–] [email protected] 1 points 1 day ago

Well the rate of airflow through the fan is at its maximum when there are no filters attached to it. Each filter likely slows down airflow if hooked up in a "series" pattern, but you're right that having these four in "parallel" will increase flow compared to one strapped directly to it. I'm sure there's a problem with reducing the airflow too much, because the fans motor would start to burn, and I'd guess that hoisting the fan up in the air rather than standing upright on the ground would improve airflow.

That being said, I'd need to do it myself and see what strapping a single filter to a fan does. I have hunch it wouldn't burn out the motor, and I imagine it'd still be effective. If the rate of airflow isn't severely reduced with a single filter, that'd just mean the same amount of air is being forced through a filter in either case (1 vs 4 filters).

Of course the single filter would wear out four times as fast so it probably won't make a difference in how many you buy in the long run. I'm just sort of rambling at this point but it's a neat concept to think about.

[–] [email protected] 6 points 3 days ago (1 children)
[–] [email protected] 1 points 3 days ago (1 children)
[–] [email protected] 1 points 3 days ago

Not the weed guy though.

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