The filters in my Corsi-Rosenthal Box look after 30 days of continuous use...

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.
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.

"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.
- “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.”
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.
- That a good idea ! Didn't think about it.

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 mean, yes.
  But like, they have to, without the filter.
- Some dirt gets pushed out and sum just stays

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!!!

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

This is a great reminder to clean my computer fans.

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

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

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.
- If you go for the 2” thick filters they breathe better and have more surface area.
- this is true. I pick up filters from shut down businesses and warehouses sometimes when people dont know what they cost and post them to fbm or craigslist and if they are higher than 13 I also put a filter for the bottom panel since I usually hang them blowing down with cords taped at the corners. even then they start to suck inward.

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
- Link? Used to have one like that but now I can't find another one
Do you have the link for it? So we can all have one.
- You're not a true lemmy unless you own The Rug
- I got it from my parents after they didn't want it anymore, but I think they got it from IKEA

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

Ya, they were brand new filters from the store. I bought them along with the box fan and duct tape.
This apartment doesnt have a HVAC system (just wall mounted AC unit) so it's doing all the air filtration.
- This is why I buy my HVAC filters in bulk 4 or 8 at a time and replace them every 3-4 months (less if there is smoke). The difference it makes in keeping the house clean is very noticable. I get very little dust accumulation except in my teens rooms because they leave their doors closed.
I buy these and swap as needed
https://www.homedepot.com/p/HDX-20-in-x-20-in-x-1-in-Standard-Pleated-Furnace-Air-Filter-FPR-5-MERV-8-12-Pack-HDXCP5-012020/332831164

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.
- Say it in a pirate accent
- Is that a portmanteau made from "arse" and "therapy"? Because I might be interested.
have you heard of the Ikea Starkvind filters? they're a bit smaller but you can tape together as many as you want
Theres a way i bet. You just need the filter dimensions to match the fan on one axis.
Can you order from Alibaba?
You can make them yourself using felt, wire and glue. Might not be exactly as effective but better than nothing.

Post a new one for comparison.

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

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.
- Flexible weather stripping for doors is good for this.

I really need to make one of these.

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.
- I feel ya. My house was miles away from the evacuation zone of the PacNW fires a little ways back, and the filters didn't last the month. We wore masks with filters rated for smoke whenever we had to go outside, and sealed every external seam, hoping the firefighters could get it under control in time. Thankfully, they're the public servants that actually know what that phrase means, and to the enth degree. I trust every one of them right alongside our Nat'l Park service members (rangers, et al), sight unseen.
  When this nation's collapse comes to your town, remember this simple rule, fellow US peeps:
  Firefighters & National Park Service? Heroes of the people, through & through.
  Cops, etc.? Shoot on sight (if that's your chosen theme for the apoc, ofc.) 😅

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

Just doing my part ground control 🫡

Can you talk about how you made this

It’s literally what you see in the picture. Just household furnace filters taped into a box with a fan. You can pick your level of filtration with the type of filters you buy.
- Does the fan suck or blow, and why? I seem to recall that the motor will burn out if you face it the wrong way.
UC Davis has a video on how to build one.

Ok. I've been looking into this a lil and there are better options than a cr box.

Housefresh has been looking into this and they recommend the nukit tempest or luggable XL or another one - think it was a Canadian brand - as the cheapest total costs over time and lowest sound and most efficient purification. All of those use regular HVAC filters which cuts down on operating cost and are quite big which cuts down electricity and sound.

So recommend getting one of those for long term use, if you have the space for it.

There's also an open source tempest that you can use a CNC for and customize to your liking with a script. https://github.com/opennukit/Nukit-Open-Air-Purifier/tree/main/Nukit%20Open%20Air%20Purifier-W(all)%20v1.0
- I have an unfinished project to make a nukit with a power knob.
  I got a cardboard proof of concept working but need to make my mark 1 out of plywood or something else.

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.

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.

I built one back when I lived in California during fire season, and then again during the pandemic. They do such a nice job making the air less gross.

I think that's about what mine looked like after 3 or 4 weeks too...

Wow that’s really quick for saturating those filters! Wildfire season is the worst.

We did one with just one filter on the intake side. Kinda like this one better. But it takes up more room than mine. I'll have to do some experimenting.

Corsi-rosenthal box is stupid efficient.

I'm viewing this post with the Thunder app and I only see one photo: a box with a fan on top. I see no filter. Is there supposed to be a second photo?

The box is the filter
What you see are 4 hepa filter plates taped together into a box, with a fan on top. The fan blows air upwards, thus creating a low pressure environment inside the box, which sucks the air through the filters - which are originally starch white.
- Yep and if you want to get really fancy, ya can put the box on stilts and put a 5th filter on the bottom!

Can you put a bag of ice in this for simple ac?

You would have to go out and buy ice, if you use your own fridge to make the ice you will have a net negative energy also just buy a cheap AC, it would save so, so much energy.
- Oh, leaving the house? Yeah sorry i don't put pants on anymore. Good call.
Oh, that's an interesting idea, not too much different from a swamp cooler actually so ya I think it would work.
My question is, where would be the optimal spot for the ice/icepacks:
Inside, at the bottom
Inside, suspended in the middle
Inside, at the top near the fan

I've put an air filter in the bedroom next to the bed. Makes nice white noise too. I also have one next to the cat's litter box. I'm thinking of putting one in the bathroom because the toilet paper makes an insane amount of lint that builds up everywhere.

My loft is so freaking hot I’m sweltering. Could something like this keep my loft cooler, the window unit is struggling to cool it off until late at night

No. This actually will heat up your apartment by a measurable amount. This is purely an air quality type thing.
- *measurable if you have some damn good instruments.
  It will put off about as much heat as a single incandescent light bulb

OP likes it dirty!

Replacing those has got to be a pain with the amount of duct tape you used. And why is there tape on the bottom?

I used the box from the box fan to create a bottom to make it a bit more sturdy for moving around and ensure more air flows through the filters instead of slipping in under the filters.
It also helped making the CR Box easier. I used it as a mount point for each filter.
I duct taped the filter to the bottom piece creating a sort of hinge that let the filter lay flat outward.
I then would prop up two filters creating a corner and tape them on the inside and outside.
Then I'd do the same with the two remaining filters. Then finally tape the final two corners.
The next step i do is optional, but it made taping the fan on top easier. I created a fan shield, which is like the bottom but a big hole in the middle. Tape that on top.
Finally, place the fan on top tape it and try to seal any gaps.
You can just cut the tape at the top along the fan, than peel the left over tape off the fan and start again. The tape on the bottom is for either a 5th filter or just a peice of cardboard across the bottom for stability.
You just cut the tape off. They last a pretty long time. I've got one going for two years intermittently here. If it looks too rough, you can take it out side and use a vacuum or air compressor to remove a lot of the surface dust.
Tape on the bottom is for the bottom panel. Usually it's just a cardboard sheet.

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