TIL about the Corsi-Rosenthal Box
this post was submitted on 08 Jul 2025
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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
It is by far the best air purifier you can get for the money.
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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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.
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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"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.
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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I thought it was for filtering weed smoke, designed by the famous grower and strain creator Ed Rosenthal.
Think it was a covid thing.
No word on ed being the rosenthal in question.
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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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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Now imagine that, but in your lungs. Yikes.
lungs are self cleaning, dirt just dosent stay in there it gets pushed out again by tiny moving hairs
... mostly into your stomach.
I have great news for you about what happens to the contents of the stomach!
dont worry they mix with the microplastics down there
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This is a great reminder to clean my computer fans.
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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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.
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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I'm just amazed it apparently took two people to think of taping 4 air filters together with a fan on top.
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Hey, I have that same rug
It really ties the room together
Yeah, well, you know, that's just, like, your opinion, man.
I have the same box fan
i have the same duct tape
Will all of you get out of my house?!?!
Nope, the air is good here. Have any beer?
I saw a couple left in the fridge. Will you grab more chips while you're up, please?
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Christ i wish we could get these filters in au at non-arserapey prices
I read that as "our-SER-uh-pee" at first. I now have a new adjective.
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Filtering can be a rabbit hole.
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.
Now it matches the rug & walls, though
Funny enough I cleaned that rug after first moving in (apartment was pre-furnished) and it looked clean for a whole day.
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