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] 3 points 20 hours ago (1 children)

These are great, but if you’re looking for something slightly less bulky, there’s a dude selling kits online using pc fans. I’ve got two and they’re pretty much a CR box in its final form. Kits come with laser cut panels, fans, grates, etc. only need to supply two filters. Way quieter than a box fan. They’re a bit pricey but worth since they can pretty much be placed anywhere.

google clean air kits.

[–] [email protected] 2 points 17 hours ago

For that money, you can buy actual air filtration units. The box fan may be noisy, but something that big is going to have massive surface area and provide a lot of filtration.

[–] [email protected] 1 points 21 hours ago

I dont mean airflow as in rate of air moving through the fan, i mean it as in volume of air being filtered.

[–] [email protected] 26 points 2 days ago (2 children)

I'm just amazed it apparently took two people to think of taping 4 air filters together with a fan on top.

[–] [email protected] 2 points 22 hours ago (1 children)

Curious why it's not 5 filters with some little toilet paper tubes or something for legs. Was it found that the fifth filter is diminishing returns?

[–] [email protected] 3 points 21 hours ago

Sounds like an argument that would take at least two meetings and a dozen emails if this were done by a company lol.

[–] [email protected] 10 points 1 day ago

They may not have been the ones who first thought of it, but the first people to publish research that shows that taping 4 air filters together with a fan works decently compared to other, non-DIY filters (where "worked decently" means does a good enough job that it's worth doing if you want a filter but can't/won't buy or build a more complex filtering system, even if it isn't as good as "proper" filtering systems)

(Tangent: I'm reminded of the "Cox-Zucker machine", a random maths thing that Cox and Zucker made together because when Cox and Zucker met at university, they realised that their names, when combined in the traditional, alphabetical order, sounded "delightfully obscene". )

[–] [email protected] 98 points 2 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 2 days ago* (last edited 2 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 2 days ago (2 children)

Think it was a covid thing.

No word on ed being the rosenthal in question.

[–] [email protected] 15 points 2 days ago (6 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

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[–] [email protected] 10 points 2 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] 19 points 2 days ago* (last edited 2 days ago) (3 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] 16 points 2 days ago

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

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[–] [email protected] 35 points 2 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!!!

[–] [email protected] 8 points 1 day ago

I think the science comes in showing that it does actually work. Like, this is so simple of an idea that I would be skeptical of if it would work if I had had the idea by myself. I'm glad that I live in a world where, if I had thought of this and wondered "is this a good idea, or am I just being dumb for thinking something so simple could work?", I am able to go online and find information and guides on this and other diy filters

[–] GlassHalfHopeful 134 points 2 days ago* (last edited 2 days ago) (2 children)
[–] [email protected] 48 points 2 days ago (1 children)
[–] [email protected] 15 points 2 days ago (8 children)

I got MERV 13 filters to help with my kids allergies. Inside the house, perfectly fine, but once outside it's sneezing and runny noses. It's amazing.

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[–] [email protected] 21 points 2 days ago (1 children)

Been aware of the general idea for a long time, but had no idea that strapping HEPA filters to a fan has a fancy name.

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

You have to cut some cardboard and use tape too. After when your solution beat every commercial solution you are allowed to name it, just to be able to shame corpo easily.

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

from huppakke:

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

take what you will from this, but it's definitely not a stick-it-to-the-corp kinda thing

[–] [email protected] 2 points 14 hours ago

Yeah I was trying a joke. It still beat commercial alternatives which I fell is a Second good reason to give it a name.

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[–] BedSharkPal 50 points 2 days ago (1 children)

Now imagine that, but in your lungs. Yikes.

[–] [email protected] 45 points 2 days ago (6 children)

lungs are self cleaning, dirt just dosent stay in there it gets pushed out again by tiny moving hairs

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[–] [email protected] 26 points 2 days ago

This is a great reminder to clean my computer fans.

[–] [email protected] 6 points 2 days ago

I really need to make one of these.

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