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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[–] GlassHalfHopeful@lemmy.ca 136 points 1 week ago* (last edited 1 week ago) (2 children)
[–] Psythik@lemmy.world 49 points 1 week ago (1 children)
[–] baldingpudenda@lemmy.world 15 points 1 week 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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[–] Korhaka@sopuli.xyz 21 points 1 week 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.

[–] Diurnambule@jlai.lu 8 points 1 week ago* (last edited 1 week ago) (4 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.

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[–] captain_aggravated@sh.itjust.works 100 points 1 week 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.

[–] EnsignWashout@startrek.website 19 points 1 week ago* (last edited 1 week 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.

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

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[–] MeThisGuy@feddit.nl 15 points 1 week ago* (last edited 1 week ago) (4 children)

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

[–] outhouseperilous@lemmy.dbzer0.com 13 points 1 week ago (2 children)

Think it was a covid thing.

No word on ed being the rosenthal in question.

[–] huppakee@feddit.nl 15 points 1 week 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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[–] prettybunnys@sh.itjust.works 10 points 1 week 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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[–] BedSharkPal@lemmy.ca 51 points 1 week ago (1 children)

Now imagine that, but in your lungs. Yikes.

[–] einfach_orangensaft@sh.itjust.works 46 points 1 week ago (3 children)

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

[–] BagOfHeavyStones@piefed.social 7 points 1 week ago (2 children)

... mostly into your stomach.

[–] Ruthalas@infosec.pub 42 points 1 week ago (1 children)

I have great news for you about what happens to the contents of the stomach!

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dont worry they mix with the microplastics down there

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[–] billwashere@lemmy.world 36 points 1 week 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!!!

[–] AnarchistArtificer@slrpnk.net 8 points 1 week 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

[–] xorollo@leminal.space 27 points 1 week ago

This is a great reminder to clean my computer fans.

[–] LovableSidekick@lemmy.world 23 points 1 week ago (3 children)

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

[–] AnarchistArtificer@slrpnk.net 10 points 1 week 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". )

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[–] Grass@sh.itjust.works 17 points 1 week ago* (last edited 1 week 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.

[–] amino@lemmy.blahaj.zone 7 points 1 week ago* (last edited 1 week 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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[–] Drekaridill@feddit.is 14 points 1 week ago (6 children)
[–] SARGE@startrek.website 17 points 1 week ago (1 children)

It really ties the room together

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[–] fmstrat@lemmy.nowsci.com 10 points 1 week ago (2 children)
[–] expatriado@lemmy.world 11 points 1 week ago (1 children)
[–] ITeeTechMonkey@lemmy.world 31 points 1 week ago (1 children)

Will all of you get out of my house?!?!

[–] Sunlightl@fedia.io 14 points 1 week ago (1 children)

Nope, the air is good here. Have any beer?

[–] Mac@mander.xyz 9 points 1 week ago

I saw a couple left in the fridge. Will you grab more chips while you're up, please?

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[–] kayzeekayzee@lemmy.blahaj.zone 12 points 1 week ago (3 children)

Those start out white?? I think it's time to replace mine.

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[–] Taleya@aussie.zone 11 points 1 week ago (5 children)

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

[–] captain_aggravated@sh.itjust.works 8 points 1 week ago (2 children)

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

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[–] Tikiporch@lemmy.world 10 points 1 week ago (1 children)

Post a new one for comparison.

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[–] jared@mander.xyz 9 points 1 week ago (1 children)

Filtering can be a rabbit hole.

[–] ITeeTechMonkey@lemmy.world 14 points 1 week ago (1 children)

Yes it can!

I was a little miffed when i went to buy the goods for this box because i couldn't get MERV 14 filters and had to settle for MERV 13.

I plan to make a frame so i can just slide filters in each side with the fan mounted on top. I'll have to figure out a means to create a nice seal between the frame and filters so the air passes through instead of around.

[–] Mastema@infosec.pub 11 points 1 week ago (1 children)

Flexible weather stripping for doors is good for this.

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