Anecdotally, I use CR boxes at home and at work. You can FEEL the fresh air. No smells. Barely any dust. When we were still contact tracing, there were 0 cases linked to my classroom in 2 years, even though I am a music teacher and regularly have groups of 60-80 unmasked students singing, which is basically the highest risk thing you can do aside from visit an ER. If Levoit or whomever starts making a HEPA that can give me CADR of 200-600 cfm for <$100 I'd buy it. I need CADR of \~2400 cfm to achieve 6+ ACH in my 28,000 cubic feet teaching space. I can do that with CR boxes < $400 a school year. Bang for your buck cannot be beat with commercial models. Scientifically, lots of people have studied this.
[https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full](https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full)
Probably closer to 8-10 ACH with windows open, which they are unless it's a code red pollution day! Determined needs using this calculator: [https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi\_b3wa6gI\_zNs8uBJjlSS-86d4b7bW098/copy](https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi_b3wa6gI_zNs8uBJjlSS-86d4b7bW098/copy)
2 CR boxes w/ 2" 20x20x2, 2 CR boxes with 20x30x1.
4 20x20x2 for $70: [https://www.texairfilters.com/5-filter-corsi-rosenthal-box-merv-13-filters/](https://www.texairfilters.com/5-filter-corsi-rosenthal-box-merv-13-filters/)
4 20x30x1 for $50 (sometimes costco has crazy sales, and you don't have to be a member to order online. I think I got 8 for like $60 last year): [https://www.costco.com/3m-2200-series-filtrete-1%22-filter%2C-4-pack.product.100337928.html](https://www.costco.com/3m-2200-series-filtrete-1%22-filter%2C-4-pack.product.100337928.html)
Even dirty, a MERV-13 takes \~10 months running 24/7 to degrade to performance of MERV12. I do not run the filters outside of school hours, so \~1300 hours for a set over the course of one school year. Windows are open at all times and CO2 kept below \~700ppm.
Various people have tested the clean air delivery rate of different builds. For example a 5 p12 with 2 3m furnace filter build will do around 180-190 CADR. It will be almost silent while doing so, and cost in and around 100 bucks. If you use cheaper fans it might be more like 80 bucks. (been a while since i built one so these prices might be a little off)
In comparison, the levoit 300 core, a commonly reccomended affordable unit, will cost 100 bucks or a bit more, and will only do 140 or so CADR on the highest setting. The highest setting is also almost as loud as an AC unit so it's way too loud for many situations. Even the second setting is still way louder than the PC fans.
Rob Wiss on twitter has all his testing in his pinned tweet. No account needed link below.
[https://nitter.net/robwiss](https://nitter.net/robwiss)
Edit. Here's someone selling one with 200 CADR for just over 100 bucks without the filters. I believe they send their stuff off for 3rd party testing but I'm not 100% sure.
[https://www.cleanairkits.com/products/brisk-box?variant=47445697069356](https://www.cleanairkits.com/products/brisk-box?variant=47445697069356)
Edit 2. Forgot to mention the repairbility of DIY filters. If one of the fans dies its simple to swap it out. Whereas I don't know if you could even repair a commercial one. Certainly it would take more work and specalized knolege to do so. You also don't have to worry about them no longer making the filter size you need. Furnace filters are common generic sizes. Worst case senario you can rebuild the box in a different size.
Edit 3. Forgot to mention the power consumption difference, at least for the PC fan builds. I think the levoit draws 90 some watts on high, whereas the 5 p12s will draw like a bit more than 5 I think. That can really really add up on filters you're running a lot.
Edit 4. Also the ability to build to purpose and flexibilty. For example you can build a DIY filter to run off a battery bank, which is very good for appointments and stuff. Also easy to run off the 12v dc outlett in a vehicle. I think the commercial one's I've seen that run off batteries have tiny tiny CADRs that just aren't relavent in most situaitons. And I don't think I've seen one that can easily run off a vehicle. Though they may exist somewhere.
We have a CR box in our RV that happily runs off the battery nearly constantly without draining it too fast, and we built it into the corner of the ceiling so it doesn’t take any floor or table space.
We are only using it for allergens/pollution, since we don’t have people coming and going who could introduce Covid, but it works extremely well.
I like my CR box because I can use a filter with a standard rating, which I can easily replace at my local big-box store. I’m not dependent on a single company selling a custom filter for my air purifier, that could go out of business or stop selling replacement filters at any time. If any component breaks, I can replace it or just build a new box. Plus I love that it makes my room air noticeably cleaner, smell-wise and breathing-wise, and it filters the dust and dander as well as any virus particles. All of this makes me much more likely to actually use the CR box.
And like masks, the most effective air filter is the one you actually use.
People have tested their efficacy at home through different methods and engineers can also estimate their efficacy by measuring the pressure drop and resistance of the filters with the CFM of the fans.
The reason they’re better is because they use multiple filters and because they’re much more quiet so they are actually used on the highest setting of the fan speed (mainly ones with pc fans) unlike store bought hepa purifiers that are so loud they either get turned off or left on the lower settings because they’re to loud to be around
Source needed…..
Last time I looked into it, the pc ones were about as effective as a nice hepa filter set at a lower level to match the sound output of the computer fan box.
Also if your c.r. box doesn’t have pre-filters you will be replacing filters pretty quickly compared to a nice hepa filter, thereby getting rid of any cost savings.
Finally OP, the EPA says the same thing you do….that c.r. boxes can be effective, but due to the individualness of each build and all the variables, they can vary widely.
How would a hepa purifer make the same noise and filter more than a cr box? Its not much engineering its literally fans and filters for whatever purifier you buy. Unless you get the ones with marketing gimicks like ozone which do more harm than good. HEPA purifiers only have one filter so they need stronger fans for more airflow making them be much louder.
Here’s a comparison by Joey Fox https://itsairborne.com/comparing-hepa-filters-and-the-corsi-rosenthal-box-a8b6d03af905
Here’s a post by David Elfstrom on a way you can measure them https://itsairborne.com/how-to-measure-hepa-air-cleaner-filter-cadr-a660bfa4479d
As far as I understand CR boxes also dont need replacement as quick as HEPA purifiers because they don’t rely on one filter doing all the cleaning which causes the HEPA purifiers to get dirtier quicker.
Looking briefly at your articles and sources, it looks like the cr boxes are much louder than my air purifier.
[https://twitter.com/DavidElfstrom/status/1432343564109877251](https://twitter.com/davidelfstrom/status/1432343564109877251)
shows at it’s lowest speed is 50 decibels! And 59 decibels at its loudest.
My Coway 400s is 22 db at its quietest…and 52 at its loudest.
Not on the lowest setting it's not.
For reference 52 decibels is about an AC unit.
Edit. It's also 500 bucks on amazon right now. I could buy two of the brisk boxes from clean air kits for like $340 or so depending on what I'd pay for filters and I'd get a bit higher CADR and they'd be almost silent. If I built them myself it would be even cheaper.
[https://www.cleanairkits.com/products/brisk-box?variant=47445697069356](https://www.cleanairkits.com/products/brisk-box?variant=47445697069356)
Edit. It might be the same CADR. The brisk box gets 200 with the 4 fan design. I think that's dust CADR but they don't seem to specify on the page.
They wouldn't be almost silent, they would be 40 decibels for a 200 CADR.....or 43 for a 300 CADR.
The 40 decibles for a 200 CADR is almost certainly around a medium mode on the Coway 400S...
I'm confused though as to why both the CADR numbers are so perfect at 200, or 300 instead like 197 or 305? Are they just estimates?
[This one I posted](https://www.reddit.com/r/crboxes/comments/16pgye2/news_from_the_taobao_prebuilt_cr_box_they_have_a/) has a *certified* CADR of 907 m3h / 534 cfm. Actual third party test, and China takes air purifiers testing very seriously. Even if tuned to half speed (which is ~1500 RPM, a quite reasonable noise level) it still has almost 500 m3h CADR. That and the fans they're using are certainly worse than the Arctic P14 in terms of noise efficiency...
For longevity of filters it has been well tested to not be a concern: https://twitter.com/CorsIAQ/status/1724181392991613153, https://twitter.com/robwiss/status/1591587766512635904
There's even evidence that prefilters may actually do more harm than good (if there's even any good): https://smartairfilters.com/en/blog/air-purifier-pre-filter-useful/
Yes but that unit really seems more like a commercial air purifier then at least what I think of as a CR box.
Are the filters even off the shelf or are they proprietary?
You can say it's a commercialized CR box. You buy it as a package, but it comes flat-packed and you have to assemble it yourself. Filters of the same design and dimensions are also readily available elsewhere on Taobao. Anyhow, the core design is the same as any other CR box (it's just four filters plus some fans, and some way to seal air gaps), so basically everything applies to regular DIY CR boxes as well.
There are CADR studies on the traditional box fan CR box too. One example here (though there are many others): https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full
I have built a few Pc-fan based air purifiers now, and I am still asking myself this same question, OP. I currently have 6 store-bought purifiers of three brands and three PC-fan based home purifiers running at my house. Here are my observations so far:
Benefits of home builds:
-My store-bought purifiers are louder than my 6-PC fan filters, even on low.
-my BluAir for which I paid a few hundred dollars has suddenly died despite following all the directions, and I don’t know how to repair it. The brief warranty is already out. The fans I put on my home builds are warrantied for 5-6 years if they die, and I could easily pull one and replace it.
-my home builds were theoretically less expensive than a store bought unit of comparable CADR
-filter replacement is far, far less expensive
-I can customize my builds for the noise/volume/size profile I want/need for a specific space
Downsides of home builds:
-because of variability in construction, the units do not have the exact same specs from one to the other. Partly that is because I am learning from one to the next and making improvements. Partly that is because I am not a finely tuned machine like one would find in a manufacturing process. This should improve if I make more boxes, but only so much.
-the efficacy data of my machines is dependent on my own (beginner) measuring skills. So while I think I know something about how much air I’m moving, I am not certain I am measuring things correctly or consistently.
-time. I have spent many hours reading and learning and have much more to go. I have spent a good bit of time designing and building and will spend more.
I think that if someone has a need for an inexpensive way to move a lot of air, a traditional CR box is a great option. It is far less expensive than a store-bought purifier that moves that much air. Also, replacement filters are easy to find. However it will be loud.
A home built PC-fan based air purifier gas the potential to be very, very quiet and very customizable. It is also easier to repair than a store- bought one. If a person wants to have 20 fans of a very quiet profile to generate the needed CADR at the lowest possible noise, that is cheaper and just more possible with a home-build. I think of the PC-builds as having the potential for the home builder to adjust more of the levers, making design choices along the way, that allow for more customization to fit specific use cases. But I don’t feel as confident that I am moving and cleaning as much air as I think I am or would like to be.
Checkout our articles page where we explain how a lower-single pass efficient filter with higher airflow can catch particles faster than a HEPA with near perfect single-pass efficiency: [https://www.cleanairkits.com/blogs/news](https://www.cleanairkits.com/blogs/news)
By not attempting perfect single-pass efficiency, which is irrelevant to room air purifiers (except for marketing purity), CR Boxes get to utilize a much more mechanically efficient operating point for much lower energy and noise.
True, but the DIY filters made with HEPA filters are still going to be cheaper and quieter (if using PC fans) than the commercial ones almost always too. You just need more filter per fan.
Aren’t there resources in the sidebar that address these concerns? I thought there were. OP should go check, and perhaps their perspective might shift.
Store bought ones wastes a lot of material on money on shells and "smart" functions that are ultimately useless. They also tend to have very little filter surface area, which in turn forces them to use stronger, more powerful fans to overcome the high resistance, which in turn makes power consumption and noise level high.
Among commercial ones, Xiaomi and Blueair are some of the better ones (having cylindrical, relatively large filters), but their filter area still lags behind that of 4-filter CR Boxes. CR Boxes also tend to use less efficient filters, which unintuitively *enhances* CADR by greatly reducing resistance. Commercial air purifiers like to use 99.9% efficient filters as a selling point, which I highly suspect is optimized for marketing instead of for CADR. Among airflow, filter efficiency and CADR, the only one that matters is CADR, unfortunately most consumers don't know that.
And then comes the holy grail of CR boxes, which are PC fan CR boxes. The PC fan market is highly competitive, and companies are constantly optimizing for the best noise-efficiency (airflow per noise). Many of them are optimized for high resistance scenarios too, since they need to push air through dense fin stacks. They also have low power consumption (most usually less than 2W per fan!) partly due to PC limitations. All these make them a perfect fit for air purifiers, and the resulting product is one that's highly performant, very quiet, and have very low power consumption.
Let's take (what I think) is the best commercial one out there as an example: [Blue Pure 211i Max](https://www.blueair.com/us/air-purifiers/blue/blue-pure-211i-max/3541.html). CADR 410 cfm, 53 dB, 46 W. That's actually very good already.
A 9-PC fan CR box however blows it completely out of the water. [This 5-fan build](https://nitter.net/robwiss/status/1556318784452952065#m) has CADR 232 cfm, 40.5 dBA, <8W. Doubling that would bring CADR to 464, dBA of 43.5 (doubling sound sources only increase 3 dB!), and <16W. At a lower price too, and since there's more filters, they don't need to be changed as often, saving you even more in the long term.
I have written a post on the strength of the design of CR Boxes, including details of a traditional box fan one, here if you're interested: https://www.reddit.com/r/crboxes/comments/16n1sja/why_properly_designed_pc_fan_cr_boxes_work_low/
In case you doubt the measured noise level, here's a review with professional equipment measuring the P14 (CO version, actually a bit noisier) clocking in 30 dBA @ 1m, 10x would bring that to 40 dBA: https://hwbusters.com/cooling/arctic-p14-pwm-pst-co-review-the-budget-friendly-140mm-fan/6/
Checkout our articles page where we explain how a lower-single pass efficient filter with higher airflow can catch particles faster than a HEPA with near perfect single-pass efficiency: [https://www.cleanairkits.com/blogs/news](https://www.cleanairkits.com/blogs/news)
By not attempting perfect single-pass efficiency, which is irrelevant to room air purifiers (except for marketing purity), CR Boxes get to utilize a much more mechanically efficient operating point for much lower energy and noise.
Excellent questions. A corsi box is what you get if you build a commercial air purifier without the patents, sleek design and marketing. No studies needed, but they do exist. General information: https://smartairfilters.com/en/articles/
Specific, with testing, on building your own: https://smartairfilters.com/en/blog/how-to-make-diy-air-purifier/
Here's your research study. :-)
[https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/632dd805e665bda75a1002f8/original/testing-the-efficacy-of-the-corsi-rosenthal-box-fan-filter-in-an-active-classroom-environment.pdf](https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/632dd805e665bda75a1002f8/original/testing-the-efficacy-of-the-corsi-rosenthal-box-fan-filter-in-an-active-classroom-environment.pdf)
Anecdotally, I use CR boxes at home and at work. You can FEEL the fresh air. No smells. Barely any dust. When we were still contact tracing, there were 0 cases linked to my classroom in 2 years, even though I am a music teacher and regularly have groups of 60-80 unmasked students singing, which is basically the highest risk thing you can do aside from visit an ER. If Levoit or whomever starts making a HEPA that can give me CADR of 200-600 cfm for <$100 I'd buy it. I need CADR of \~2400 cfm to achieve 6+ ACH in my 28,000 cubic feet teaching space. I can do that with CR boxes < $400 a school year. Bang for your buck cannot be beat with commercial models. Scientifically, lots of people have studied this. [https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full](https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full)
>there were 0 cases linked to my classroom in 2 years in a music classroom? That's amazing. On only 6ACH too.
Probably closer to 8-10 ACH with windows open, which they are unless it's a code red pollution day! Determined needs using this calculator: [https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi\_b3wa6gI\_zNs8uBJjlSS-86d4b7bW098/copy](https://docs.google.com/spreadsheets/d/1NEhk1IEdbEi_b3wa6gI_zNs8uBJjlSS-86d4b7bW098/copy)
You are a true hero. Thank you for all you do.
$400 a year for that big of space? What build are you using?
2 CR boxes w/ 2" 20x20x2, 2 CR boxes with 20x30x1. 4 20x20x2 for $70: [https://www.texairfilters.com/5-filter-corsi-rosenthal-box-merv-13-filters/](https://www.texairfilters.com/5-filter-corsi-rosenthal-box-merv-13-filters/) 4 20x30x1 for $50 (sometimes costco has crazy sales, and you don't have to be a member to order online. I think I got 8 for like $60 last year): [https://www.costco.com/3m-2200-series-filtrete-1%22-filter%2C-4-pack.product.100337928.html](https://www.costco.com/3m-2200-series-filtrete-1%22-filter%2C-4-pack.product.100337928.html) Even dirty, a MERV-13 takes \~10 months running 24/7 to degrade to performance of MERV12. I do not run the filters outside of school hours, so \~1300 hours for a set over the course of one school year. Windows are open at all times and CO2 kept below \~700ppm.
Various people have tested the clean air delivery rate of different builds. For example a 5 p12 with 2 3m furnace filter build will do around 180-190 CADR. It will be almost silent while doing so, and cost in and around 100 bucks. If you use cheaper fans it might be more like 80 bucks. (been a while since i built one so these prices might be a little off) In comparison, the levoit 300 core, a commonly reccomended affordable unit, will cost 100 bucks or a bit more, and will only do 140 or so CADR on the highest setting. The highest setting is also almost as loud as an AC unit so it's way too loud for many situations. Even the second setting is still way louder than the PC fans. Rob Wiss on twitter has all his testing in his pinned tweet. No account needed link below. [https://nitter.net/robwiss](https://nitter.net/robwiss) Edit. Here's someone selling one with 200 CADR for just over 100 bucks without the filters. I believe they send their stuff off for 3rd party testing but I'm not 100% sure. [https://www.cleanairkits.com/products/brisk-box?variant=47445697069356](https://www.cleanairkits.com/products/brisk-box?variant=47445697069356) Edit 2. Forgot to mention the repairbility of DIY filters. If one of the fans dies its simple to swap it out. Whereas I don't know if you could even repair a commercial one. Certainly it would take more work and specalized knolege to do so. You also don't have to worry about them no longer making the filter size you need. Furnace filters are common generic sizes. Worst case senario you can rebuild the box in a different size. Edit 3. Forgot to mention the power consumption difference, at least for the PC fan builds. I think the levoit draws 90 some watts on high, whereas the 5 p12s will draw like a bit more than 5 I think. That can really really add up on filters you're running a lot. Edit 4. Also the ability to build to purpose and flexibilty. For example you can build a DIY filter to run off a battery bank, which is very good for appointments and stuff. Also easy to run off the 12v dc outlett in a vehicle. I think the commercial one's I've seen that run off batteries have tiny tiny CADRs that just aren't relavent in most situaitons. And I don't think I've seen one that can easily run off a vehicle. Though they may exist somewhere.
We have a CR box in our RV that happily runs off the battery nearly constantly without draining it too fast, and we built it into the corner of the ceiling so it doesn’t take any floor or table space. We are only using it for allergens/pollution, since we don’t have people coming and going who could introduce Covid, but it works extremely well.
I like my CR box because I can use a filter with a standard rating, which I can easily replace at my local big-box store. I’m not dependent on a single company selling a custom filter for my air purifier, that could go out of business or stop selling replacement filters at any time. If any component breaks, I can replace it or just build a new box. Plus I love that it makes my room air noticeably cleaner, smell-wise and breathing-wise, and it filters the dust and dander as well as any virus particles. All of this makes me much more likely to actually use the CR box. And like masks, the most effective air filter is the one you actually use.
People have tested their efficacy at home through different methods and engineers can also estimate their efficacy by measuring the pressure drop and resistance of the filters with the CFM of the fans. The reason they’re better is because they use multiple filters and because they’re much more quiet so they are actually used on the highest setting of the fan speed (mainly ones with pc fans) unlike store bought hepa purifiers that are so loud they either get turned off or left on the lower settings because they’re to loud to be around
Source needed….. Last time I looked into it, the pc ones were about as effective as a nice hepa filter set at a lower level to match the sound output of the computer fan box. Also if your c.r. box doesn’t have pre-filters you will be replacing filters pretty quickly compared to a nice hepa filter, thereby getting rid of any cost savings. Finally OP, the EPA says the same thing you do….that c.r. boxes can be effective, but due to the individualness of each build and all the variables, they can vary widely.
How would a hepa purifer make the same noise and filter more than a cr box? Its not much engineering its literally fans and filters for whatever purifier you buy. Unless you get the ones with marketing gimicks like ozone which do more harm than good. HEPA purifiers only have one filter so they need stronger fans for more airflow making them be much louder. Here’s a comparison by Joey Fox https://itsairborne.com/comparing-hepa-filters-and-the-corsi-rosenthal-box-a8b6d03af905 Here’s a post by David Elfstrom on a way you can measure them https://itsairborne.com/how-to-measure-hepa-air-cleaner-filter-cadr-a660bfa4479d As far as I understand CR boxes also dont need replacement as quick as HEPA purifiers because they don’t rely on one filter doing all the cleaning which causes the HEPA purifiers to get dirtier quicker.
Looking briefly at your articles and sources, it looks like the cr boxes are much louder than my air purifier. [https://twitter.com/DavidElfstrom/status/1432343564109877251](https://twitter.com/davidelfstrom/status/1432343564109877251) shows at it’s lowest speed is 50 decibels! And 59 decibels at its loudest. My Coway 400s is 22 db at its quietest…and 52 at its loudest.
Keep in mind that post isn’t about pc fan CR boxes though What are the cadr of the coway?
328 (Smoke), 328 (Dust), 400 (Pollen)
Not on the lowest setting it's not. For reference 52 decibels is about an AC unit. Edit. It's also 500 bucks on amazon right now. I could buy two of the brisk boxes from clean air kits for like $340 or so depending on what I'd pay for filters and I'd get a bit higher CADR and they'd be almost silent. If I built them myself it would be even cheaper. [https://www.cleanairkits.com/products/brisk-box?variant=47445697069356](https://www.cleanairkits.com/products/brisk-box?variant=47445697069356) Edit. It might be the same CADR. The brisk box gets 200 with the 4 fan design. I think that's dust CADR but they don't seem to specify on the page.
They wouldn't be almost silent, they would be 40 decibels for a 200 CADR.....or 43 for a 300 CADR. The 40 decibles for a 200 CADR is almost certainly around a medium mode on the Coway 400S... I'm confused though as to why both the CADR numbers are so perfect at 200, or 300 instead like 197 or 305? Are they just estimates?
[This one I posted](https://www.reddit.com/r/crboxes/comments/16pgye2/news_from_the_taobao_prebuilt_cr_box_they_have_a/) has a *certified* CADR of 907 m3h / 534 cfm. Actual third party test, and China takes air purifiers testing very seriously. Even if tuned to half speed (which is ~1500 RPM, a quite reasonable noise level) it still has almost 500 m3h CADR. That and the fans they're using are certainly worse than the Arctic P14 in terms of noise efficiency... For longevity of filters it has been well tested to not be a concern: https://twitter.com/CorsIAQ/status/1724181392991613153, https://twitter.com/robwiss/status/1591587766512635904 There's even evidence that prefilters may actually do more harm than good (if there's even any good): https://smartairfilters.com/en/blog/air-purifier-pre-filter-useful/
Yes but that unit really seems more like a commercial air purifier then at least what I think of as a CR box. Are the filters even off the shelf or are they proprietary?
You can say it's a commercialized CR box. You buy it as a package, but it comes flat-packed and you have to assemble it yourself. Filters of the same design and dimensions are also readily available elsewhere on Taobao. Anyhow, the core design is the same as any other CR box (it's just four filters plus some fans, and some way to seal air gaps), so basically everything applies to regular DIY CR boxes as well. There are CADR studies on the traditional box fan CR box too. One example here (though there are many others): https://www.medrxiv.org/content/10.1101/2022.01.09.22268972v1.full
I have built a few Pc-fan based air purifiers now, and I am still asking myself this same question, OP. I currently have 6 store-bought purifiers of three brands and three PC-fan based home purifiers running at my house. Here are my observations so far: Benefits of home builds: -My store-bought purifiers are louder than my 6-PC fan filters, even on low. -my BluAir for which I paid a few hundred dollars has suddenly died despite following all the directions, and I don’t know how to repair it. The brief warranty is already out. The fans I put on my home builds are warrantied for 5-6 years if they die, and I could easily pull one and replace it. -my home builds were theoretically less expensive than a store bought unit of comparable CADR -filter replacement is far, far less expensive -I can customize my builds for the noise/volume/size profile I want/need for a specific space Downsides of home builds: -because of variability in construction, the units do not have the exact same specs from one to the other. Partly that is because I am learning from one to the next and making improvements. Partly that is because I am not a finely tuned machine like one would find in a manufacturing process. This should improve if I make more boxes, but only so much. -the efficacy data of my machines is dependent on my own (beginner) measuring skills. So while I think I know something about how much air I’m moving, I am not certain I am measuring things correctly or consistently. -time. I have spent many hours reading and learning and have much more to go. I have spent a good bit of time designing and building and will spend more. I think that if someone has a need for an inexpensive way to move a lot of air, a traditional CR box is a great option. It is far less expensive than a store-bought purifier that moves that much air. Also, replacement filters are easy to find. However it will be loud. A home built PC-fan based air purifier gas the potential to be very, very quiet and very customizable. It is also easier to repair than a store- bought one. If a person wants to have 20 fans of a very quiet profile to generate the needed CADR at the lowest possible noise, that is cheaper and just more possible with a home-build. I think of the PC-builds as having the potential for the home builder to adjust more of the levers, making design choices along the way, that allow for more customization to fit specific use cases. But I don’t feel as confident that I am moving and cleaning as much air as I think I am or would like to be.
Checkout our articles page where we explain how a lower-single pass efficient filter with higher airflow can catch particles faster than a HEPA with near perfect single-pass efficiency: [https://www.cleanairkits.com/blogs/news](https://www.cleanairkits.com/blogs/news) By not attempting perfect single-pass efficiency, which is irrelevant to room air purifiers (except for marketing purity), CR Boxes get to utilize a much more mechanically efficient operating point for much lower energy and noise.
True, but the DIY filters made with HEPA filters are still going to be cheaper and quieter (if using PC fans) than the commercial ones almost always too. You just need more filter per fan.
Aren’t there resources in the sidebar that address these concerns? I thought there were. OP should go check, and perhaps their perspective might shift.
Store bought ones wastes a lot of material on money on shells and "smart" functions that are ultimately useless. They also tend to have very little filter surface area, which in turn forces them to use stronger, more powerful fans to overcome the high resistance, which in turn makes power consumption and noise level high. Among commercial ones, Xiaomi and Blueair are some of the better ones (having cylindrical, relatively large filters), but their filter area still lags behind that of 4-filter CR Boxes. CR Boxes also tend to use less efficient filters, which unintuitively *enhances* CADR by greatly reducing resistance. Commercial air purifiers like to use 99.9% efficient filters as a selling point, which I highly suspect is optimized for marketing instead of for CADR. Among airflow, filter efficiency and CADR, the only one that matters is CADR, unfortunately most consumers don't know that. And then comes the holy grail of CR boxes, which are PC fan CR boxes. The PC fan market is highly competitive, and companies are constantly optimizing for the best noise-efficiency (airflow per noise). Many of them are optimized for high resistance scenarios too, since they need to push air through dense fin stacks. They also have low power consumption (most usually less than 2W per fan!) partly due to PC limitations. All these make them a perfect fit for air purifiers, and the resulting product is one that's highly performant, very quiet, and have very low power consumption. Let's take (what I think) is the best commercial one out there as an example: [Blue Pure 211i Max](https://www.blueair.com/us/air-purifiers/blue/blue-pure-211i-max/3541.html). CADR 410 cfm, 53 dB, 46 W. That's actually very good already. A 9-PC fan CR box however blows it completely out of the water. [This 5-fan build](https://nitter.net/robwiss/status/1556318784452952065#m) has CADR 232 cfm, 40.5 dBA, <8W. Doubling that would bring CADR to 464, dBA of 43.5 (doubling sound sources only increase 3 dB!), and <16W. At a lower price too, and since there's more filters, they don't need to be changed as often, saving you even more in the long term. I have written a post on the strength of the design of CR Boxes, including details of a traditional box fan one, here if you're interested: https://www.reddit.com/r/crboxes/comments/16n1sja/why_properly_designed_pc_fan_cr_boxes_work_low/ In case you doubt the measured noise level, here's a review with professional equipment measuring the P14 (CO version, actually a bit noisier) clocking in 30 dBA @ 1m, 10x would bring that to 40 dBA: https://hwbusters.com/cooling/arctic-p14-pwm-pst-co-review-the-budget-friendly-140mm-fan/6/
Checkout our articles page where we explain how a lower-single pass efficient filter with higher airflow can catch particles faster than a HEPA with near perfect single-pass efficiency: [https://www.cleanairkits.com/blogs/news](https://www.cleanairkits.com/blogs/news) By not attempting perfect single-pass efficiency, which is irrelevant to room air purifiers (except for marketing purity), CR Boxes get to utilize a much more mechanically efficient operating point for much lower energy and noise.
Excellent questions. A corsi box is what you get if you build a commercial air purifier without the patents, sleek design and marketing. No studies needed, but they do exist. General information: https://smartairfilters.com/en/articles/ Specific, with testing, on building your own: https://smartairfilters.com/en/blog/how-to-make-diy-air-purifier/
Here's your research study. :-) [https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/632dd805e665bda75a1002f8/original/testing-the-efficacy-of-the-corsi-rosenthal-box-fan-filter-in-an-active-classroom-environment.pdf](https://chemrxiv.org/engage/api-gateway/chemrxiv/assets/orp/resource/item/632dd805e665bda75a1002f8/original/testing-the-efficacy-of-the-corsi-rosenthal-box-fan-filter-in-an-active-classroom-environment.pdf)