"Use the box the fan came in."
January 13, 2023 3:30 PM Subscribe
The Corsi-Rosenthal Box: or, how to build a DIY portable air cleaner with four filters and a box fan
(bok bok)
posted by away for regrooving at 3:52 PM on January 13, 2023
posted by away for regrooving at 3:52 PM on January 13, 2023
eponysterical?
I like how one of the inventors is the chief executive of an air filter company. On the one hand of course he wants you to buy more filters but on the other it is nice to see that someone that high up is still doing productive work.
Nitpick: the article says to use 4 20x20x1 filters but the photos and video clearly show 20x20x2 filters.
posted by any portmanteau in a storm at 3:56 PM on January 13, 2023 [8 favorites]
I like how one of the inventors is the chief executive of an air filter company. On the one hand of course he wants you to buy more filters but on the other it is nice to see that someone that high up is still doing productive work.
Nitpick: the article says to use 4 20x20x1 filters but the photos and video clearly show 20x20x2 filters.
posted by any portmanteau in a storm at 3:56 PM on January 13, 2023 [8 favorites]
The dead simple way to do this is to stick a 20x20 filter on the intake side of your box fan. If the fan is on, you don't even need tape. The downside is that this will significantly shorten the life of your fan. But given these fans can be pretty cheap compared to 4 MERV filters I think it's worth the simplicity.
posted by muddgirl at 4:00 PM on January 13, 2023 [6 favorites]
posted by muddgirl at 4:00 PM on January 13, 2023 [6 favorites]
Nitpick: the article says to use 4 20x20x1 filters but the photos and video clearly show 20x20x2 filters.
...and the audio on the video addresses this directly.
posted by NotMyselfRightNow at 4:13 PM on January 13, 2023
...and the audio on the video addresses this directly.
posted by NotMyselfRightNow at 4:13 PM on January 13, 2023
This seems like an honestly good thing, but the smooth shopping-channel musak they use really takes away from the video's credibility.
posted by Greg_Ace at 4:14 PM on January 13, 2023 [2 favorites]
posted by Greg_Ace at 4:14 PM on January 13, 2023 [2 favorites]
(and raised its annoyance factor)
posted by Greg_Ace at 4:15 PM on January 13, 2023 [1 favorite]
posted by Greg_Ace at 4:15 PM on January 13, 2023 [1 favorite]
I spent a couple of hours the other day putting one of these together. It's pretty simple – four filters, arranged as the vertical sides of a cube with the airflow arrows pointing inward, with a cardboard square as the bottom and a 20-inch box fan (pointing up) as the top. All seams and joins thoroughly sealed with duct tape so the air that the fan pulls in has to go through the filters instead of through any gaps.
Took it into work today and put it in my cubicle, where it seems to be working fine. Unfortunately, not many people in my workplace wear masks, and with the box running I now feel a lot better about taking my mask down occasionally for a drink of coffee or water.
This site has a lot of information about it, including links to videos showing how to assemble one: CleanAirCrew: DIY box fan filters – Corsi-Rosenthal box
posted by Lexica at 4:15 PM on January 13, 2023 [17 favorites]
Took it into work today and put it in my cubicle, where it seems to be working fine. Unfortunately, not many people in my workplace wear masks, and with the box running I now feel a lot better about taking my mask down occasionally for a drink of coffee or water.
This site has a lot of information about it, including links to videos showing how to assemble one: CleanAirCrew: DIY box fan filters – Corsi-Rosenthal box
posted by Lexica at 4:15 PM on January 13, 2023 [17 favorites]
But a good HEPA cleaner costs between $300 and $600.
The supplies to make one filter box cost me $127: $30 for the 20-inch box fan, about $90 for a four-pack of Merv-13 filters.
How often the filters need to be replaced will depend on use.
I'm not gonna say this isn't cool, because it is cool. But how frequently you need to change those filters kind of makes the difference between a great lifehack and Vimes Boots Theory.
posted by Reyturner at 4:18 PM on January 13, 2023 [19 favorites]
The supplies to make one filter box cost me $127: $30 for the 20-inch box fan, about $90 for a four-pack of Merv-13 filters.
How often the filters need to be replaced will depend on use.
I'm not gonna say this isn't cool, because it is cool. But how frequently you need to change those filters kind of makes the difference between a great lifehack and Vimes Boots Theory.
posted by Reyturner at 4:18 PM on January 13, 2023 [19 favorites]
You still need to change the filters on those HEPA cleaners, and a set of new filters can set you back $300-$500 bucks.
posted by phooky at 4:26 PM on January 13, 2023 [10 favorites]
posted by phooky at 4:26 PM on January 13, 2023 [10 favorites]
The dead simple way to do this is to stick a 20x20 filter on the intake side of your box fan.
I tried this out, and basically got zero airflow. I don't think box fans are designed to deal with the surface area of only a single air filter. The other configs of the C-R box take up a ton of space.
posted by meowzilla at 4:29 PM on January 13, 2023 [6 favorites]
I tried this out, and basically got zero airflow. I don't think box fans are designed to deal with the surface area of only a single air filter. The other configs of the C-R box take up a ton of space.
posted by meowzilla at 4:29 PM on January 13, 2023 [6 favorites]
But a good HEPA cleaner costs between $300 and $600.
...You still need to change the filters on those HEPA cleaners, and a set of new filters can set you back $300-$500 bucks.
Huh? You can get adequate HEPA air purifiers for normal-sized rooms for $100-$150, so about the same as the estimated cost here. Replacement filters (they come with a set) are $60 a pop. Seems to me that Corsi-Rosenthal boxes are one of those items whose tenure in our consciousness is based more on the perception that they're a cool science hack rather than real usefulness (at least in an environment where you can readily buy legit air purifiers for a reasonable price--which arguably didn't exist at the time they were invented).
posted by praemunire at 5:07 PM on January 13, 2023 [6 favorites]
...You still need to change the filters on those HEPA cleaners, and a set of new filters can set you back $300-$500 bucks.
Huh? You can get adequate HEPA air purifiers for normal-sized rooms for $100-$150, so about the same as the estimated cost here. Replacement filters (they come with a set) are $60 a pop. Seems to me that Corsi-Rosenthal boxes are one of those items whose tenure in our consciousness is based more on the perception that they're a cool science hack rather than real usefulness (at least in an environment where you can readily buy legit air purifiers for a reasonable price--which arguably didn't exist at the time they were invented).
posted by praemunire at 5:07 PM on January 13, 2023 [6 favorites]
I've been running fans + box filters for years to clean the air of cat hair and litter box dust.
posted by rebent at 5:31 PM on January 13, 2023 [6 favorites]
posted by rebent at 5:31 PM on January 13, 2023 [6 favorites]
Some folks have been putting together units out of 12v PC power supply fans and using two rather than four filters; the resulting shape is like a suitcase with filters on the large sides and fans on the small. They are much quieter (which is kind of important for school/office/workplace use), still move a lot of air, and only a little more expensive. These people are selling completed units and kits. Not as quick and simple as the duct-taped cube, for sure. But halfway between there and the wacky expensive HEPA units with far cheaper filter replacement cost.
We use several IKEA FORNUFTIG units, which are $75 each in Canada. They are quiet, have decent filter surface area, and move quite a bit of air. Replacement filters are cheap, and you can get an activated carbon insert to remove odour (helpful if you're dealing with an indoor smoker).
posted by seanmpuckett at 5:41 PM on January 13, 2023 [11 favorites]
We use several IKEA FORNUFTIG units, which are $75 each in Canada. They are quiet, have decent filter surface area, and move quite a bit of air. Replacement filters are cheap, and you can get an activated carbon insert to remove odour (helpful if you're dealing with an indoor smoker).
posted by seanmpuckett at 5:41 PM on January 13, 2023 [11 favorites]
There is way, way more filter media on the 4 filter box than any standalone hepa filter targeted at residential use. Filter media life time is essentially directly proportional area divided by flow so if a couple purifiers both flow the same but one has twice the area then that one's filters will last twice as long. $90 vs $60 is an overwhelming win for the box.
If 2" thick filters are less than double the price of 1" filters you are probably better off with the 2" filters (space requirements notwithstanding).
I have a similar set up filtering air in my wood shop (about 550 square feet) but powered with a 1250 CFM squirrel cage blower out of a furnace and it takes a good 10-15 minutes to filter dust out of the air. Works pretty good but the fan I'm using is designed for that sort of static pressure.
In an office environment the most effective use would be to direct the hopefully virus free airflow at your face rather than trying to clean the entire office. Having the filter draw contaminated air into your space and then directing the clean air away might even be counter productive in a large office.
posted by Mitheral at 5:44 PM on January 13, 2023 [11 favorites]
If 2" thick filters are less than double the price of 1" filters you are probably better off with the 2" filters (space requirements notwithstanding).
I have a similar set up filtering air in my wood shop (about 550 square feet) but powered with a 1250 CFM squirrel cage blower out of a furnace and it takes a good 10-15 minutes to filter dust out of the air. Works pretty good but the fan I'm using is designed for that sort of static pressure.
In an office environment the most effective use would be to direct the hopefully virus free airflow at your face rather than trying to clean the entire office. Having the filter draw contaminated air into your space and then directing the clean air away might even be counter productive in a large office.
posted by Mitheral at 5:44 PM on January 13, 2023 [11 favorites]
C-R Boxes were all the rage in 2018 in the first bad year of California wildfires. You couldn't find a box fan or MERV filter anywhere, and HEPA purifiers were as rare as hen's teeth.
They're a fun DIY/school project, but trying to convince normal people that they should put this large loud duct tape/cardboard contraption into their homes (instead of a slick Blueair unit) seems misguided.
posted by meowzilla at 5:47 PM on January 13, 2023 [3 favorites]
They're a fun DIY/school project, but trying to convince normal people that they should put this large loud duct tape/cardboard contraption into their homes (instead of a slick Blueair unit) seems misguided.
posted by meowzilla at 5:47 PM on January 13, 2023 [3 favorites]
I have a CR box in my office (I'm a professor at a university) and one in the classroom I teach in. So far I haven't gotten COVID as far as I know. I'm in Alaska, where buildings traditionally have been optimized to keep outside cold air out and warm inside air in, which doesn't lead to fantastic ventilation. The university just did a bunch of HVAC work in my building over break, it'll be interesting to see what effect it has if any. I'm still planning on running the CR box during class. It's not too bad if I run it at its lowest setting; if it's on high it's a little noisy.
posted by leahwrenn at 6:22 PM on January 13, 2023 [8 favorites]
posted by leahwrenn at 6:22 PM on January 13, 2023 [8 favorites]
You couldn't find a box fan or MERV filter anywhere, and HEPA purifiers were as rare as hen's teeth.
As a solution for market failure, they're perfectly reasonable. It's just that the market failure has been resolved.
posted by praemunire at 6:51 PM on January 13, 2023 [1 favorite]
As a solution for market failure, they're perfectly reasonable. It's just that the market failure has been resolved.
posted by praemunire at 6:51 PM on January 13, 2023 [1 favorite]
How often the filters need to be replaced will depend on use.
Yeah this is kind of sort of very important. If it costs $90 for four filters and you have to replace them every...month? Every two weeks? Every six months? And how are you to know that the filters need replacing?
posted by zardoz at 6:55 PM on January 13, 2023 [1 favorite]
Yeah this is kind of sort of very important. If it costs $90 for four filters and you have to replace them every...month? Every two weeks? Every six months? And how are you to know that the filters need replacing?
posted by zardoz at 6:55 PM on January 13, 2023 [1 favorite]
I've been running fans + box filters for years to clean the air of cat hair and litter box dust.
Yep — I made one of these 25 years ago and I’ll be damned if I call it a Corsi-Rosenthal Box.
I have similar feelings about the whole “KonMari method” to describe decluttering, simplifying, and keeping only the things that make you feel good.
I’m sure this makes me petty, or something.
*shakes fist at sky*
posted by darkstar at 7:53 PM on January 13, 2023 [2 favorites]
Yep — I made one of these 25 years ago and I’ll be damned if I call it a Corsi-Rosenthal Box.
I have similar feelings about the whole “KonMari method” to describe decluttering, simplifying, and keeping only the things that make you feel good.
I’m sure this makes me petty, or something.
*shakes fist at sky*
posted by darkstar at 7:53 PM on January 13, 2023 [2 favorites]
Ok,
1) you want the contaminated side of the filter on the inside of the box so that contaiminants stay away from users/bystanders
2) you want the path from the exhaust side of the fan and the intake side of the fan to be as long as possible and to go through as many of your living/working spaces as possible. Because if the air only needs to travel an inch to get back to the pump/fan it wi take that shortest path and render most.of your room unchanged.
3) washable reuseable merv filters exist for reasonable prices.
4) your good indoor air should be at slightly positive pressure to your bad air so that leaks are good air eacaping instead if bad air entering your clean space
Thus, the box fan should be put in a window, blowing air into the filter box, it will look like you mounted an A/C unit the opposite way. Then seal the window gaps as you would for any appliance. Then that room is the best air, and rooms further from that room are less well served. As an added bonus this will help lower indoor air polluntants down to the (unacceptavly high but less thab inside) level of pullution outside.
posted by anecdotal_grand_theory at 8:20 PM on January 13, 2023 [3 favorites]
1) you want the contaminated side of the filter on the inside of the box so that contaiminants stay away from users/bystanders
2) you want the path from the exhaust side of the fan and the intake side of the fan to be as long as possible and to go through as many of your living/working spaces as possible. Because if the air only needs to travel an inch to get back to the pump/fan it wi take that shortest path and render most.of your room unchanged.
3) washable reuseable merv filters exist for reasonable prices.
4) your good indoor air should be at slightly positive pressure to your bad air so that leaks are good air eacaping instead if bad air entering your clean space
Thus, the box fan should be put in a window, blowing air into the filter box, it will look like you mounted an A/C unit the opposite way. Then seal the window gaps as you would for any appliance. Then that room is the best air, and rooms further from that room are less well served. As an added bonus this will help lower indoor air polluntants down to the (unacceptavly high but less thab inside) level of pullution outside.
posted by anecdotal_grand_theory at 8:20 PM on January 13, 2023 [3 favorites]
Can the stress on the fan motor and the heightened axial load on the bearings beyond what they are designed for be mitigated by putting multiple fans in series? When I did this I sandwiched a filter between two box fans.
posted by BrotherCaine at 8:26 PM on January 13, 2023 [1 favorite]
posted by BrotherCaine at 8:26 PM on January 13, 2023 [1 favorite]
The First Annual CorsiRosenthal Box Awards (Twitter)
posted by MonkeyToes at 8:29 PM on January 13, 2023 [3 favorites]
posted by MonkeyToes at 8:29 PM on January 13, 2023 [3 favorites]
Huh? You can get adequate HEPA air purifiers for normal-sized rooms for $100-$150, so about the same as the estimated cost here.
The instructions claim that you can get 300-400 ft^3 per minute from this box and the HEPA filter to which you linked does that about every 20 minutes. OTOH, the HEPA filter is small and cute and (probably) very quiet.
you want the contaminated side of the filter on the inside of the box so that contaiminants stay away from users/bystanders
They appear to have done this the other way, with the contaminated side on the outside.
posted by It's Never Lurgi at 9:05 PM on January 13, 2023 [2 favorites]
The instructions claim that you can get 300-400 ft^3 per minute from this box and the HEPA filter to which you linked does that about every 20 minutes. OTOH, the HEPA filter is small and cute and (probably) very quiet.
you want the contaminated side of the filter on the inside of the box so that contaiminants stay away from users/bystanders
They appear to have done this the other way, with the contaminated side on the outside.
posted by It's Never Lurgi at 9:05 PM on January 13, 2023 [2 favorites]
The dead simple way to do this is to stick a 20x20 filter on the intake side of your box fan. If the fan is on, you don't even need tape.
This is very much not true; you still need to tape the sides of the filter to the side of the fan. Otherwise, the fan is pulling a lot of the air from the sides and not through the filter.
User error in the building and sealing of either the 1-filter or 4-filter design is probably the biggest problem here. You don't want someone thinking their setup is filtering when it actually isn't. But this does seem like a fairly straightforward construction. I'd like to know what the benefits of the boxy, 4-filter design of the Cori-Rosenthal has on just taping a filter to the intake of a Lasko box fan. I assume it's easier on the fan motor and filters more effectively. (I hope so, because 4x the filters is quite a boost in price.)
From this HVAC association website:
With the understanding that COVID-19-containing particles can stay in the air long enough to move into the breathing space and into HVAC systems, the desire to filter these particles out of the air is strong. ASHRAE is recommending that MERV 13 filters be used where possible, with MERV-A 13-A or MERV 14 preferred.
Lately, I have seen this used as a faulty reason for saying that filters don’t catch COVID-19 because the virus itself is less than 0.3 µm. In practice, the virus is almost always embedded in particles that are much bigger, with recent reporting indicating much of the COVID-19 virus may occur mostly in particles in the 1 µm to 5 µm size range. So, the filter efficiency below 0.3 µm is completely irrelevant.
posted by AlSweigart at 9:33 PM on January 13, 2023 [2 favorites]
This is very much not true; you still need to tape the sides of the filter to the side of the fan. Otherwise, the fan is pulling a lot of the air from the sides and not through the filter.
User error in the building and sealing of either the 1-filter or 4-filter design is probably the biggest problem here. You don't want someone thinking their setup is filtering when it actually isn't. But this does seem like a fairly straightforward construction. I'd like to know what the benefits of the boxy, 4-filter design of the Cori-Rosenthal has on just taping a filter to the intake of a Lasko box fan. I assume it's easier on the fan motor and filters more effectively. (I hope so, because 4x the filters is quite a boost in price.)
From this HVAC association website:
With the understanding that COVID-19-containing particles can stay in the air long enough to move into the breathing space and into HVAC systems, the desire to filter these particles out of the air is strong. ASHRAE is recommending that MERV 13 filters be used where possible, with MERV-A 13-A or MERV 14 preferred.
Lately, I have seen this used as a faulty reason for saying that filters don’t catch COVID-19 because the virus itself is less than 0.3 µm. In practice, the virus is almost always embedded in particles that are much bigger, with recent reporting indicating much of the COVID-19 virus may occur mostly in particles in the 1 µm to 5 µm size range. So, the filter efficiency below 0.3 µm is completely irrelevant.
posted by AlSweigart at 9:33 PM on January 13, 2023 [2 favorites]
I looked into making a CR box for my university classes, but ended up buying a commercial product instead because MERV filters are not easily/cheaply available here in Japan and the costs didn't add up.
Re commercial HEPA air purifiers, I found this tool useful when helping my parents in Australia work out what product would be best for them:
https://cleanairstars.com/filters/
posted by mydonkeybenjamin at 9:41 PM on January 13, 2023 [4 favorites]
Re commercial HEPA air purifiers, I found this tool useful when helping my parents in Australia work out what product would be best for them:
https://cleanairstars.com/filters/
posted by mydonkeybenjamin at 9:41 PM on January 13, 2023 [4 favorites]
Prior-ish art from the Wirecutter using a single filter taped to a fan, back in 2019 when our biggest air concern was smoke.
https://www.nytimes.com/wirecutter/blog/how-to-diy-an-air-purifier/
posted by Nonsteroidal Anti-Inflammatory Drug at 9:57 PM on January 13, 2023 [1 favorite]
https://www.nytimes.com/wirecutter/blog/how-to-diy-an-air-purifier/
posted by Nonsteroidal Anti-Inflammatory Drug at 9:57 PM on January 13, 2023 [1 favorite]
I have 5 of these setups, 4 with single 20x20x5 Merv 12-16 filters on them, and one with 2 5" Merv 16's in a triangle configuration. All the fans are cheap $20-30 ones bought online in the last 5-7 years. 3 of them run 24/7 on low, and have for several years. The filters really only get obviously dirty after either a year or more of use, or being in a dusty carpeted area. None of the fans have died or shown any signs of aging.
COVID aside, I live in Portland and had these going during the couple summers of fire/smoke hell that were off the charts, and the filters COMPLETELY knocked down the smoke and smell indoors, even in poorly built and insulated buildings.
I'm a fan.
posted by Nosmot at 10:27 PM on January 13, 2023 [23 favorites]
COVID aside, I live in Portland and had these going during the couple summers of fire/smoke hell that were off the charts, and the filters COMPLETELY knocked down the smoke and smell indoors, even in poorly built and insulated buildings.
I'm a fan.
posted by Nosmot at 10:27 PM on January 13, 2023 [23 favorites]
The instructions claim that you can get 300-400 ft^3 per minute from this box and the HEPA filter to which you linked does that about every 20 minutes. OTOH, the HEPA filter is small and cute and (probably) very quiet.
So, in theory, if you put it together exactly right (which, you know, it is a kludge)...it goes up to 11. I'm pretty sure there are diminishing returns in there somewhere, especially given that placing either a purifier or a box optimally is probably impossible. For most people's purposes, this problem is now solved. I'm not anti-box, nor anti-tinkering! Have at it, have fun. But its usefulness in present-day civilian life is being exaggerated. (I actually thought it was cheaper...there's an argument for a $50 version. $100-$150 startup will be too much for some. But I'll take their word on the prices.)
posted by praemunire at 10:55 PM on January 13, 2023
So, in theory, if you put it together exactly right (which, you know, it is a kludge)...it goes up to 11. I'm pretty sure there are diminishing returns in there somewhere, especially given that placing either a purifier or a box optimally is probably impossible. For most people's purposes, this problem is now solved. I'm not anti-box, nor anti-tinkering! Have at it, have fun. But its usefulness in present-day civilian life is being exaggerated. (I actually thought it was cheaper...there's an argument for a $50 version. $100-$150 startup will be too much for some. But I'll take their word on the prices.)
posted by praemunire at 10:55 PM on January 13, 2023
I don't care what people call it, I just wish I would SEE filters out in the wild.
My dentist had one in every room. Staff are all masked. He told me they've had no cases that they know of.
I carry a portable hepa filter with me at work. Had it in a meeting with our provost, and he made some kind of positive remark. I said it would be a worthwhile $200 to spend on every classroom on campus. On the U budget scale, it's a drop in the bucket.
Haven't seen any.
posted by Dashy at 4:46 AM on January 14, 2023 [10 favorites]
My dentist had one in every room. Staff are all masked. He told me they've had no cases that they know of.
I carry a portable hepa filter with me at work. Had it in a meeting with our provost, and he made some kind of positive remark. I said it would be a worthwhile $200 to spend on every classroom on campus. On the U budget scale, it's a drop in the bucket.
Haven't seen any.
posted by Dashy at 4:46 AM on January 14, 2023 [10 favorites]
I'd be very worried that cheep Lasco fan would overheat and possible catch fire. I don't know if those fans has any sort of safety cut off.
posted by james33 at 4:53 AM on January 14, 2023
posted by james33 at 4:53 AM on January 14, 2023
My allergist instructed me to make sure to buy a “True HEPA” filter. Some of them are “HEPA like” and aren’t worth crap.
posted by Fleebnork at 6:02 AM on January 14, 2023 [1 favorite]
posted by Fleebnork at 6:02 AM on January 14, 2023 [1 favorite]
I’m a fan of CR boxes as well. In August when my youngest kid came down with COVID (thanks, high school with no masking!) I built one to scrub our air while we all scattered to different rooms. We managed to limit the spread to jut one other person, leaving me and my oldest kid well and able to move him into his freshman dorm.
So of course his roommate came down with COVID two weeks later.
Worse, his roommate came back despite still coughing, because the CDC and college said five days was enough. Cue an online Lowe’s order so my kid could build a CR box. He once again escaped getting sick.
Anecdata, sure, but I’m haunted by the early paper that showed how air flow contributed to the spread in a restaurant. I double checked the numbers and confirmed that I’m getting a full air exchange every twenty minutes or less in the rooms I’ve used them in. In the absence of, you know, actual society-wide fixes to indoor ventilation, I’ll keep this as part of my toolkit.
posted by sgranade at 6:51 AM on January 14, 2023 [9 favorites]
So of course his roommate came down with COVID two weeks later.
Worse, his roommate came back despite still coughing, because the CDC and college said five days was enough. Cue an online Lowe’s order so my kid could build a CR box. He once again escaped getting sick.
Anecdata, sure, but I’m haunted by the early paper that showed how air flow contributed to the spread in a restaurant. I double checked the numbers and confirmed that I’m getting a full air exchange every twenty minutes or less in the rooms I’ve used them in. In the absence of, you know, actual society-wide fixes to indoor ventilation, I’ll keep this as part of my toolkit.
posted by sgranade at 6:51 AM on January 14, 2023 [9 favorites]
CR boxes let you actually get enough airflow to be protective while not being too loud. Most small HEPA systems are too loud to talk over when they're running on "medium/high", and they don't generate enough air change equivalents on low.
It's fine for the contaminants to be "visible. It's safest for the airflow to be directed vertically.
Aerosol-transmitted diseases could go the way of waterborne ones, if we could kind of get our shit together even just a little bit.
ps- if you don't like the name, because neither Corsi nor Rosenthal invented that geometry, allow me to remind you of Stigler's Law of Eponymy!
posted by MengerSponge at 9:27 AM on January 14, 2023 [4 favorites]
It's fine for the contaminants to be "visible. It's safest for the airflow to be directed vertically.
Aerosol-transmitted diseases could go the way of waterborne ones, if we could kind of get our shit together even just a little bit.
ps- if you don't like the name, because neither Corsi nor Rosenthal invented that geometry, allow me to remind you of Stigler's Law of Eponymy!
posted by MengerSponge at 9:27 AM on January 14, 2023 [4 favorites]
Ugh, fine. I am hereby naming the configuration of having a pair of socks rolled up together with the elastic opening of one sock everted to enclose the roll as the “Darkstar Method”.
Soon, everyone will referring to the Darkstar Method. “Do you Darkstar your socks?” they’ll ask. “Of course!” they’ll respond, “It sparks joy!” Then they will get a Cease-and-Desist from Marie Kondo.
I may be sending out an email soon calling for submissions to the First Annual Darkstar Socks Competition. I’m sure there are opportunities for merch tie-ins.
Seriously, though, the version I made of the Lasko Fan Filter was with only two filters. The fan was sitting horizontally, and I used cardboard triangles on the top and bottom, with the filters on the two sides. Kept the fan on low and it seemed to work okay.
posted by darkstar at 10:22 AM on January 14, 2023 [2 favorites]
Soon, everyone will referring to the Darkstar Method. “Do you Darkstar your socks?” they’ll ask. “Of course!” they’ll respond, “It sparks joy!” Then they will get a Cease-and-Desist from Marie Kondo.
I may be sending out an email soon calling for submissions to the First Annual Darkstar Socks Competition. I’m sure there are opportunities for merch tie-ins.
Seriously, though, the version I made of the Lasko Fan Filter was with only two filters. The fan was sitting horizontally, and I used cardboard triangles on the top and bottom, with the filters on the two sides. Kept the fan on low and it seemed to work okay.
posted by darkstar at 10:22 AM on January 14, 2023 [2 favorites]
I just wish I would SEE filters out in the wild. My dentist had one in every room. Staff are all masked. He told me they've had no cases that they know of.
My theater got six HEPA filters in 2021. Most of them are gone from the building ("they needed to get the filters replaced," but I don't think they've been put back) and the only one I could find a few weeks ago when I went looking started beeping incessantly when I turned it on, and the stage manager said that needs to be changed too. I talked to her about it, but I doubt that's been fixed. Even then, I usually had to go turn the one in the dressing room on every day when they were in there.
Otherwise, nobody uses them, you're right there. It would be such a help. Literally nobody will do anything any more.
(Still loving my portable filter, though!)
posted by jenfullmoon at 10:27 AM on January 14, 2023 [1 favorite]
My theater got six HEPA filters in 2021. Most of them are gone from the building ("they needed to get the filters replaced," but I don't think they've been put back) and the only one I could find a few weeks ago when I went looking started beeping incessantly when I turned it on, and the stage manager said that needs to be changed too. I talked to her about it, but I doubt that's been fixed. Even then, I usually had to go turn the one in the dressing room on every day when they were in there.
Otherwise, nobody uses them, you're right there. It would be such a help. Literally nobody will do anything any more.
(Still loving my portable filter, though!)
posted by jenfullmoon at 10:27 AM on January 14, 2023 [1 favorite]
I like the name “Corsi–Rosenthal Box” because it reminds me of the Einstein–Podolsky–Rosen Paradox.
(Darkstar–Kondo Pair’o’socks?)
posted by mbrubeck at 10:29 AM on January 14, 2023 [6 favorites]
(Darkstar–Kondo Pair’o’socks?)
posted by mbrubeck at 10:29 AM on January 14, 2023 [6 favorites]
...having a pair of socks rolled up together with the elastic opening of one sock everted to enclose the roll...
This is definitely not the Kondo method. She says socks don't want to be 'potatoes'.
I, however, think they do want to be potatoes, so that's what I do, but henceforth will call them Darkstars.
But back to the topic at hand. I'm curious that 1 filter would cause more resistance than 4 filters, which was implied earlier.
My first thought was to use 3 filters so I could put a closed side up against a wall for more space. (Or even a 2-filter box I could put in a corner)
posted by MtDewd at 10:44 AM on January 14, 2023 [1 favorite]
This is definitely not the Kondo method. She says socks don't want to be 'potatoes'.
I, however, think they do want to be potatoes, so that's what I do, but henceforth will call them Darkstars.
But back to the topic at hand. I'm curious that 1 filter would cause more resistance than 4 filters, which was implied earlier.
My first thought was to use 3 filters so I could put a closed side up against a wall for more space. (Or even a 2-filter box I could put in a corner)
posted by MtDewd at 10:44 AM on January 14, 2023 [1 favorite]
... socks don't want to be 'potatoes'
My socks prefer to be a pile of spaghetti. but I don't wash them in salted water
posted by Greg_Ace at 11:12 AM on January 14, 2023
My socks prefer to be a pile of spaghetti. but I don't wash them in salted water
posted by Greg_Ace at 11:12 AM on January 14, 2023
I'm curious that 1 filter would cause more resistance than 4 filters
Imagine blowing through a standard straw (0.25" diameter), then through one of the same length but half an inch in diameter. I hope a rooted-in-reality imagination finds it much easier to blow through the bigger straw.
posted by achrise at 11:48 AM on January 14, 2023 [3 favorites]
Imagine blowing through a standard straw (0.25" diameter), then through one of the same length but half an inch in diameter. I hope a rooted-in-reality imagination finds it much easier to blow through the bigger straw.
posted by achrise at 11:48 AM on January 14, 2023 [3 favorites]
I like the name “Corsi–Rosenthal Box” because it reminds me of the Einstein–Podolsky–Rosen Paradox.
That was close to my thought as well - not the paradox exactly, but that the box name is clearly the name of some sort of multiverse connecting portal, not something as prosaic as an air cleaner. It probably is the pairing of names and ‘Rosen’ tickling that bit of memory that ‘Einstein-Rosen Bridge’ lives in.
posted by Jon Mitchell at 1:30 PM on January 14, 2023 [1 favorite]
That was close to my thought as well - not the paradox exactly, but that the box name is clearly the name of some sort of multiverse connecting portal, not something as prosaic as an air cleaner. It probably is the pairing of names and ‘Rosen’ tickling that bit of memory that ‘Einstein-Rosen Bridge’ lives in.
posted by Jon Mitchell at 1:30 PM on January 14, 2023 [1 favorite]
A couple questions:
1. How does the thickness of the filter impact the quality? I got the 4 inch thick filter that's nicely accordianed instead of a 2 inch thick filter because i figured it would lower the air pressure thus be easier on the fan.
2. How does thickness and configuration of filters impact the number of hours they can be in use before being replaced? If I have a 4 filter cube, do the filters last 4 times longer than a single filter?
Does the 4-inch thick filter have 2x as much square foot of filter as a 2-in thick filter? If so, will it last twice as long before needing to be replaced?
3. Is there an easy math to compare these filters against Honeywell fancy filters? Do filter folk talk about.... Cubic feet of air filtered per hour? Or, % air cleaned per hour in a 100 meter cube? Cost of filtering one room for one day?
4. How does electricity use for these filters compare against Honeywell filters?
5. Are there "heavy duty" or long-lasting fans that would be a good idea to invest in? I am on my second box fan filter, but my first one lasted longer than the Honeywell I bought.
posted by rebent at 2:41 PM on January 14, 2023 [1 favorite]
1. How does the thickness of the filter impact the quality? I got the 4 inch thick filter that's nicely accordianed instead of a 2 inch thick filter because i figured it would lower the air pressure thus be easier on the fan.
2. How does thickness and configuration of filters impact the number of hours they can be in use before being replaced? If I have a 4 filter cube, do the filters last 4 times longer than a single filter?
Does the 4-inch thick filter have 2x as much square foot of filter as a 2-in thick filter? If so, will it last twice as long before needing to be replaced?
3. Is there an easy math to compare these filters against Honeywell fancy filters? Do filter folk talk about.... Cubic feet of air filtered per hour? Or, % air cleaned per hour in a 100 meter cube? Cost of filtering one room for one day?
4. How does electricity use for these filters compare against Honeywell filters?
5. Are there "heavy duty" or long-lasting fans that would be a good idea to invest in? I am on my second box fan filter, but my first one lasted longer than the Honeywell I bought.
posted by rebent at 2:41 PM on January 14, 2023 [1 favorite]
Round duct fans for venting grow rooms run about 50-100 and have high 90-309 cubic feet per minute venting, are quiet* (.5-2 sonnes) and there are decent carbon filters, hepa filters and pre-hepa dust screens for them usually in 4" and 6" diameters.
Especially if smoke is an issue having an active carbon stage is useful. Vivo sun brand maybe takes 70watts on high.
The evil jeff jorgensen sells them on his rainforest website.
Generally the trade offs on filters are: the more junk it filters out, the harder it is to pull/push air through it. The more surface area, the easier to push or pull the same amount of air.
Some fans are built to move a lot of air but only if they are getting no resistance (think box fans and ceiling fans) some fans are built to move less air but can push it harder against resistance, typically these are duct fans or blowers.
posted by anecdotal_grand_theory at 11:47 PM on January 14, 2023
Especially if smoke is an issue having an active carbon stage is useful. Vivo sun brand maybe takes 70watts on high.
The evil jeff jorgensen sells them on his rainforest website.
Generally the trade offs on filters are: the more junk it filters out, the harder it is to pull/push air through it. The more surface area, the easier to push or pull the same amount of air.
Some fans are built to move a lot of air but only if they are getting no resistance (think box fans and ceiling fans) some fans are built to move less air but can push it harder against resistance, typically these are duct fans or blowers.
posted by anecdotal_grand_theory at 11:47 PM on January 14, 2023
The real issue is this: we need to let go of the idea of fresh air as the default and commit to living, working and traveling in air that we make safe. Most of us no longer drink straight from puddles, streams, gutters or ponds without filtration and treatment.
wildfires, viruses, allergens, potentially rafioactive salt-lake dust, formaldehyde, etc...
Our species evolve in a world that is gone, we were born into a chemical industrial boom-town and the ecological consequences of our exploding numbers, our devestating consumption, our interconnected world and our terrible weapons means that we need to re-colonise a poisoned earth and it is going to take water and air filters, and many other adjustments to save ourselves, our companion species, and as much of the biodiversity as we can.
Wild animals are breathing this contaminated air too. They are getting coronavirus, they are getting inflamed from smog, they are getting endocrine disrupted too.
We wear sandals and sit on chairs because it is not possible to make a soft carpet out of the whole earth. Now we must make masks and room filters a part of our essential clothing/furniture.
We should get good at this now, before CO2 reaches levels that cause cognitive impairment.
posted by anecdotal_grand_theory at 11:56 PM on January 14, 2023 [3 favorites]
wildfires, viruses, allergens, potentially rafioactive salt-lake dust, formaldehyde, etc...
Our species evolve in a world that is gone, we were born into a chemical industrial boom-town and the ecological consequences of our exploding numbers, our devestating consumption, our interconnected world and our terrible weapons means that we need to re-colonise a poisoned earth and it is going to take water and air filters, and many other adjustments to save ourselves, our companion species, and as much of the biodiversity as we can.
Wild animals are breathing this contaminated air too. They are getting coronavirus, they are getting inflamed from smog, they are getting endocrine disrupted too.
We wear sandals and sit on chairs because it is not possible to make a soft carpet out of the whole earth. Now we must make masks and room filters a part of our essential clothing/furniture.
We should get good at this now, before CO2 reaches levels that cause cognitive impairment.
posted by anecdotal_grand_theory at 11:56 PM on January 14, 2023 [3 favorites]
Corsi-Rosenthal Box
The University gym I worked out last year had them all over the place. This plus the school having a vaccine & booster mandate was part of why I chose to overpay to workout there.
They got rid of the fans right around when the Democratic party decided abandoning everything but vax-pushing and pretending the pandemic was over was the key to the electoral victory.
I cancelled my gym membership.
posted by srboisvert at 4:48 AM on January 15, 2023 [8 favorites]
The University gym I worked out last year had them all over the place. This plus the school having a vaccine & booster mandate was part of why I chose to overpay to workout there.
They got rid of the fans right around when the Democratic party decided abandoning everything but vax-pushing and pretending the pandemic was over was the key to the electoral victory.
I cancelled my gym membership.
posted by srboisvert at 4:48 AM on January 15, 2023 [8 favorites]
Ive found that if you want to do a single filter design you can use a 4x20x20 filter instead of a 1x20x20 and 3 years later I’m still on the first box fan.
posted by interogative mood at 9:46 AM on January 15, 2023 [5 favorites]
posted by interogative mood at 9:46 AM on January 15, 2023 [5 favorites]
Some of them are “HEPA like” and aren’t worth crap.
Keep in mind that the MERV filters discussed for making C-R boxes are usually worse than HEPA filters.
What is a MERV rating? (EPA)
MERV 13: 0.30-1.0 Microns: less than or equal to 50% (better for larger/smaller)
HEPA: 99.97% of particles in the 0.3-micron range (better for larger/smaller)
So it's not quite right to directly compare the airflow between a filter using HEPA and one using MERV 13. Depending on the particle size, the MERV 13 filter may be capturing substantially less than the HEPA.
But if there's many multiples of air being pushed through the MERV filters, the numbers may come close. (I don't have the math skills to determine this.) There is also evidence that covid particles mostly travel on other particles that are not in the 0.3 micron, meaning that the MERV filters can perform substantially better. Unlike an N95 or N100 mask, air indoors has several chances to be captured by the filter, but a mask you have the one shot. And of course, having something that works partially well is better than not having the thing that works very well.
posted by meowzilla at 8:42 PM on January 15, 2023
Keep in mind that the MERV filters discussed for making C-R boxes are usually worse than HEPA filters.
What is a MERV rating? (EPA)
MERV 13: 0.30-1.0 Microns: less than or equal to 50% (better for larger/smaller)
HEPA: 99.97% of particles in the 0.3-micron range (better for larger/smaller)
So it's not quite right to directly compare the airflow between a filter using HEPA and one using MERV 13. Depending on the particle size, the MERV 13 filter may be capturing substantially less than the HEPA.
But if there's many multiples of air being pushed through the MERV filters, the numbers may come close. (I don't have the math skills to determine this.) There is also evidence that covid particles mostly travel on other particles that are not in the 0.3 micron, meaning that the MERV filters can perform substantially better. Unlike an N95 or N100 mask, air indoors has several chances to be captured by the filter, but a mask you have the one shot. And of course, having something that works partially well is better than not having the thing that works very well.
posted by meowzilla at 8:42 PM on January 15, 2023
By the way, today I folded laundry, and I put away 13 Darkstars.
posted by MtDewd at 9:10 AM on January 16, 2023 [1 favorite]
posted by MtDewd at 9:10 AM on January 16, 2023 [1 favorite]
I found this academic research via Wikipedia:
In terms of first cost, cost per unit of air cleaning was $0.17-$0.24 per Clean Air Delivery Rate, depending on speed. This was significantly less expensive than commercially available small portable air cleaners that cost at least $0.71 per CADR.
CADR is a combined measure of both volume and filtration. It is the cubic feet per minute (CFM) of air that has had all the particles of a given size distribution removed. (Wikipedia)
Because the four-filter configuration contains such a large filter surface area, the filters are expected to provide up to a year of service. Performance degradation (i.e., reduced airflow) due the filter loading was not tested.
Another study found "While CR Boxes were deployed, concentrations of seven PFAS (N-EtFOSE, N-EtFOSA, FBSA, PFBS, PFHxS, PFOS, PFNA) were 28–61% lower and concentrations of five phthalates (DMP, DEP, DiBP, BBzP, DCHP) were 29–62% lower."
And apparently, Ford partnered with a fan maker to design this cardboard stand for a 1-filter system
All that said, I wish someone would make a formula that says how many CR Cubes I need to maximally filter all dangerous elements from the air, how often the filters should be changed, how many hours per day they should run, and how much it costs per year to do so.
posted by rebent at 12:22 PM on January 16, 2023 [1 favorite]
In terms of first cost, cost per unit of air cleaning was $0.17-$0.24 per Clean Air Delivery Rate, depending on speed. This was significantly less expensive than commercially available small portable air cleaners that cost at least $0.71 per CADR.
CADR is a combined measure of both volume and filtration. It is the cubic feet per minute (CFM) of air that has had all the particles of a given size distribution removed. (Wikipedia)
Because the four-filter configuration contains such a large filter surface area, the filters are expected to provide up to a year of service. Performance degradation (i.e., reduced airflow) due the filter loading was not tested.
Another study found "While CR Boxes were deployed, concentrations of seven PFAS (N-EtFOSE, N-EtFOSA, FBSA, PFBS, PFHxS, PFOS, PFNA) were 28–61% lower and concentrations of five phthalates (DMP, DEP, DiBP, BBzP, DCHP) were 29–62% lower."
And apparently, Ford partnered with a fan maker to design this cardboard stand for a 1-filter system
All that said, I wish someone would make a formula that says how many CR Cubes I need to maximally filter all dangerous elements from the air, how often the filters should be changed, how many hours per day they should run, and how much it costs per year to do so.
posted by rebent at 12:22 PM on January 16, 2023 [1 favorite]
GROUNDBREAKING + EPIC TEST: Bioengineers 👩🔬👨🔬 at CDC conducted world’s 1st “crash test” of Do-It-Yourself (DIY) air purifiers to check if they cab stop viruses 🦠 between test dummies. It’s like NHTSA running crash tests with dummies in cars 🚗 🚙. (1/16) https://www.sciencedirect.com/science/article/pii/S0360132322011507[Thread Reader]
pic.twitter.com/Ncm8WmHg0K— Devabhaktuni "Sri" Srikrishna (@sri_srikrishna) January 7, 2023
posted by ob1quixote at 7:30 AM on January 17, 2023 [4 favorites]
Thanks, ob1quixote!
posted by MonkeyToes at 3:52 PM on January 17, 2023 [1 favorite]
posted by MonkeyToes at 3:52 PM on January 17, 2023 [1 favorite]
Over the last couple years I've donated tens of these to my son's school. Of course, the school doesn't want these; they maintain that their existing air quality is good enough. But teachers sure do want them, and teachers have a fair amount of leeway because of the labor shortage. So if you want to keep your kids safer, don't talk to your school about donating these; just talk to your teachers.
In terms of filter lifetime, it depends on how dusty/hairy the environment is that the box is operating in, and how long the box is operating per day (duty cycle). If you turn the box on only when people are present, the filters will last longer. The estimates I've seen go between 4 to 12 months.
I am extremely curious about whether that could be extended, though, by having a removable cover like cheesecloth over the filters. The cheesecloth may catch e.g. dog hair that would otherwise be dirtying the filters.
posted by a snickering nuthatch at 6:20 AM on February 2, 2023 [2 favorites]
In terms of filter lifetime, it depends on how dusty/hairy the environment is that the box is operating in, and how long the box is operating per day (duty cycle). If you turn the box on only when people are present, the filters will last longer. The estimates I've seen go between 4 to 12 months.
I am extremely curious about whether that could be extended, though, by having a removable cover like cheesecloth over the filters. The cheesecloth may catch e.g. dog hair that would otherwise be dirtying the filters.
posted by a snickering nuthatch at 6:20 AM on February 2, 2023 [2 favorites]
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I want to be all "yay" for this, but at the same time, every time I read instructions on it, my brain just...doesn't get it. This is supposed to be filters for dummies, but I'm a dummy. But also, construction is not my skill once it goes farther than yarn or Legos.
posted by jenfullmoon at 3:52 PM on January 13, 2023 [4 favorites]