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] 34 points 3 days ago (1 children)

I totally did not realize how much real science was behind these things. I mean this design is so simple and obvious, it seems like something I would throw together because it just looks like it “should” work. And according to the research I just read they are very efficient and effective. Super cool!!!

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[–] [email protected] 6 points 3 days ago

I really need to make one of these.

[–] [email protected] 17 points 3 days ago* (last edited 3 days ago) (1 children)

make sure you get merv 13 or higher for smoke. the filters get gross fast even with 8 but you can tell the difference when you breathe.

I have 2 to 4 of these going at all times and the 8s are full time and 13+ are periodic unless fire season.

[–] [email protected] 7 points 3 days ago* (last edited 3 days ago) (2 children)

correct me if I'm wrong but anything higher than MERV 13 has diminishing returns because of increased resistance. instead of going for increased MERV I recommend getting thicker MERV 13 because of their bigger surface area.

CR boxes rely on raw total air volume and increased ACH vs HEPA which relies on filtering as much air as possible on the first pass.

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[–] [email protected] 5 points 3 days ago (1 children)

Good job, Captain Lovell. That’s some Apollo 13-level engineering right there.

[–] [email protected] 4 points 3 days ago

Just doing my part ground control 🫡

[–] [email protected] 98 points 3 days ago (2 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) (4 children)

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

[–] [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 (2 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

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[–] [email protected] 15 points 3 days ago (4 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] 6 points 3 days ago (2 children)
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[–] [email protected] 19 points 3 days ago* (last edited 3 days ago) (2 children)

I'm going to start talking in vague terms about my own designs for a "Corsi-Rosenthal Box" when I want to sound smart.

It'll be great if anyone bothers to look it up.

[–] [email protected] 5 points 3 days ago* (last edited 3 days ago) (1 children)

“My Corsi-Rosenthal Box is designed to efficiently accelerate particles inwards. The particles are then ‘captured’ using a special filtering technique, and separated from the air molecules which are allowed through.”

[–] [email protected] 7 points 3 days ago

It’s removing particulates though.

So you could call it and “anti-particulate vertical fluid acceleration device” maybe.

[–] [email protected] 16 points 3 days ago

I mean, it sounds like an Einstein-Rosen bridge.

[–] [email protected] 11 points 3 days ago (5 children)

Christ i wish we could get these filters in au at non-arserapey prices

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

Can you order from Alibaba?

[–] [email protected] 2 points 3 days ago

Theres a way i bet. You just need the filter dimensions to match the fan on one axis.

[–] [email protected] 5 points 3 days ago

have you heard of the Ikea Starkvind filters? they're a bit smaller but you can tape together as many as you want

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

You can make them yourself using felt, wire and glue. Might not be exactly as effective but better than nothing.

[–] [email protected] 8 points 3 days ago (2 children)

I read that as "our-SER-uh-pee" at first. I now have a new adjective.

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

Say it in a pirate accent

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

Is that a portmanteau made from "arse" and "therapy"? Because I might be interested.

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

Post a new one for comparison.

[–] [email protected] 2 points 3 days ago

You can eference the outer edges for a satisfying before/after.

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