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Also known as a Corsi-Rosenthal box, this DIY method of building your own air filter with MERV13 furnace filters and a box fan are an easy and cost-effective way to help clear indoor air from airborne virus particles, wildfire smoke, pollen, dust, and more! If you can seal a box, you can build one (or 100!) of these! Note: quickstart wildfire guide here How to clean the air from wildfire smoke * * * Table of Contents * Image / Video Gallery * Video: How to effectively ventilate classrooms using fans, HEPA filters or Corsi-Rosenthal box fans and monitors * Start here * Illustrated Guide * The Fan Shroud * Choosing filters * Performance * Round Fan alternate design * Travel DIY Air filter * Modification: Screen as “prefilter” * FAQ – Frequently Asked Questions * Video: Box Fan Filter build tutorial – Spanish * Video: A Fourth Grader Explains How to Build a DIY Corsi/Rosenthal Box Air Cleaner * Mass production! * Common concerns addressed * In the news: ## Image / Video Gallery This gallery includes photos of builds, creative modifications, instructional images, as well as videos. Click through tags below to load more. * All * 1filter (1) * 2filter (5) * 4filter (22) * 5filter (14) * art (10) * featured (23) * instructions (19) * modifications (9) * spanish (1) * videos (3) Download Download Download Download Download Download Download Download Download Download Download Download Play Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Download Play Download Play Download Play Download Play Download Download Download Download Download Download Download Download Play * * * ## Video: How to effectively ventilate classrooms using fans, HEPA filters or Corsi-Rosenthal box fans and monitors Cleaning indoor air properly greatly reduces infections by airborne viruses, like COVID-19. This video explains it all very well! Via CleanClassroomAir.com * * * # How to build a Corsi-Rosenthal box fan filter ## Start here A Variation on the “Box Fan with MERV 13 Filter” Air Cleaner Article by Jim Rosenthal **Read about it in WIRED:** https://www.wired.com/story/could-a-janky-jury-rigged-air-purifier-help-fight-covid-19/ **Construction Guide** : More details, including filter brands to avoid, here: encycla.com/Corsi-Rosenthal_Cube (by Philip Neustrom) (hint: Filterbuy MERV-13, prevalent on Amazon, have not tested well) * * * ## Illustrated Guide by Amanda H @ughberta > Updated the images to include both top fan and side fan configurations and clarification on direction of air flow pic.twitter.com/YkHOhbFNEF > > — Amanda Hu (@amandalhu) July 26, 2021 ## The Fan Shroud An optional part of a box fan filter is the fan shroud, or covered fan corners. Covering corners of a square box fan closes gaps and improves efficiency of the fan. See Jim Rosenthal’s article about it here. Use cardboard or duct tape. Testing to optimize fan shroud size. David Elfstrom found a 13.5 to 14.25 inch diameter opening to work best with a Utilitech brand fan. Lasko fans work best with a 15 inch fan shroud. shroud size for box fan air filter > Important! Get the most out of your #boxfanfilter with a shroud on the outlet. Improves inlet flow & reduces power and noise. I've found optimum size for two models. Same final flow. > Utilitech/Hurricane: 13.5" dia, +47% flow > Lasko Comfort: 15" dia, +38% flow pic.twitter.com/TX9mBO7Pbq > > — David Elfstrom (@DavidElfstrom) August 18, 2021 * * * ## Choosing filters David Elfstrom advises “keep an eye out for local sales on the 20x20x1 or 20x25x1 Filtrete 1900 and box fans“ To build with 2 inch deep filters, use (3) 20x20x2 and (2) 16x20x2 You can order a full set of high-quality MERV13 filters to make this air purifier here: https://www.texairfilters.com/filters-for-box-fan-and-merv-13-filters-air-cleaner These 2 inch deep filters (compared to typical 1 inch) provide greater surface area for filtration, better air flow, quieter operation, and longer filter life. * * * ## Performance The Corsi-Rosenthal box (single filter tested, full cube would be even better!) performs very well! It is the most cost effective air cleaner on Marwa Zaatari’s chart! > 📢📢📢 Updated Air Cleaner Chart: > > I added the DIY CR box as optimized by @DavidElfstrom. > > Look at this beauty!! @kprather88 @JimRosenthal4 > It is the most cost effective purifier on the chart. > > See below 🧵 comparison to intellipure(tm) /Blueair ™/needle point bp ionization https://t.co/ZY399PlYKR pic.twitter.com/febD3sh00b > > — Marwa Zaatari (@marwa_zaatari) August 23, 2021 * * * **From Bill Bahnfleth, Chair – ASHRAE Epidemic Task Force** > The CR box is not specifically referenced in ASHRAE guidance, but they are completely consistent with guidance about upgrading filters and using portable air cleaners to improve clean air delivery rate where needed. You can certainly quote me on that. > > — Bill Bahnfleth (@WBahnfleth) December 10, 2021 source: https://twitter.com/WBahnfleth/status/1469454061225316353?s=20 > Bottom line – Use of DIY air cleaners with MERV 13 or better filters that are well constructed is consistent with ASHRAE’s requirements for effectiveness and safety and can help to mitigate airborne exposure that causes Covid-19. 7/7 > > — Bill Bahnfleth (@WBahnfleth) December 11, 2021 source: https://twitter.com/WBahnfleth/status/1469781099043864583 * * * **CR Boxes in Johns Hopkins “Ventilation: Vital Tool to Reduce Spread”** > They’re also listed in the Johns Hopkins “Ventilation: Vital Tool to Reduce Spread” paper here : https://t.co/IBbba4jXtg pic.twitter.com/qgTCPW1YB6 > > — Marina A. Creed (@MarinaC_Dyb) December 11, 2021 source: https://twitter.com/MarinaC_Dyb/status/1469469896664829952?s=20 * * * ## Round Fan alternate design Not all parts of the world have box fans available. This international team has worked out an alternate design using a round fan! > Are you looking to make a #CorsiRosenthalBox but box fans aren't available in your area? We've worked out a great design with a round fan! Picture instructions are in this thread, but we have a video tutorial here! https://t.co/LslZXzNcEY#COVIDisAirborne #FreshAirRAndD https://t.co/yVgSS6PtJu > > — Amanda Hu (@amandalhu) October 22, 2021 * * * ## Travel DIY Air filter > Personal Air Filters cleanaircrew.org/personal-air-filters * * * ## Modification: Screen as “prefilter” This modification, adding fiberglass screen material, can keep pet hair out of filters and prolong their useful life, with barely noticeable flow reduction! > Here's the fiberglass screen added to a 20×20 based cube. Barely noticable flow reduction, just 1.27% loss!! > Mesh is 18×16 per inch, diameter 0.011, made by Adfors. There's other options avail but this is most economical, and it doesn't impede flow. pic.twitter.com/SsJKN32vQr > > — David Elfstrom (@DavidElfstrom) November 14, 2021 * * * ## FAQ – Frequently Asked Questions New comprehensive FAQ page here! > THE Corsi/Rosenthal Box FAQ Also, tons of details and FAQs in this excellent comprehensive thread by Lazarus Long. * * * ## Video: Box Fan Filter build tutorial – Spanish source: AleHSalcedo2 ## Video: A Fourth Grader Explains How to Build a DIY Corsi/Rosenthal Box Air Cleaner source: @gbignami Watch more videos * * * > Wow putting this collage together made me happy. This is what happens when people put their minds into helping protect kids in schools. Yes, anyone can build a Corsi-Rosenthal box — as @JimRosenthal4 says–if you can tape a package to mail, you can build one of these. (1/7) pic.twitter.com/4Q4YHGhfTQ > > — Kimberly Prather, Ph.D. (@kprather88) August 30, 2021 ## Mass production! Check out how Rosie @BkPhilanthropy assembled and distributed 100 air filters! > We emailed school district union presidents and spread the invitation for free #corsirosenthalboxes that way. > > A 2 hour distribution window was set. This location was ideal, making pick up a drive -through service. pic.twitter.com/uryDIEHkYY > > — Rosie🌻Healthy Air Evangelist🌻 (@BkPhilanthropy) October 12, 2021 https://twitter.com/BkPhilanthropy/status/1447905430366265349?s=20 Download the printable PDF of the insert they included with the filters! C-R Box Insert BkPhilanthropyDownload * * * **Dr. Prather with UCSanDiego** > All hands on deck! 🛠️ This week, @UCSanDiego's @kprather88 & volunteers made air filtration boxes out of AC filters & box fans to place indoors on campus—an effort to help stop the spread of #COVID19 & other viruses. This collab involved Scripps, @UCSDPhySci & @ucsdbiosciences. pic.twitter.com/7VNBCWHV5A > > — Scripps Institution of Oceanography (@Scripps_Ocean) September 24, 2021 > Contraption for cutting 250 shrouds…13.5 inch hole. pic.twitter.com/iUN4tpEnRj > > — Kimberly Prather, Ph.D. (@kprather88) September 22, 2021 * * * **Brown University** **Students unite to take a hands-on, DIY approach to improving air quality** An event hosted by Brown’s School of Public Health brought students together to build low-cost, highly effective Corsi-Rosenthal cubes as air filters that will augment existing filtration systems at Brown. www.brown.edu/news/2021-11-19/diy * * * > Gallery of tweets showing mass production of #corsirosenthalbox fan filters – to add more tag @davidelfstrom https://t.co/yvCJMLPozJ > > — David Elfstrom (@DavidElfstrom) September 22, 2021 * * * ## Common concerns addressed Developed by @amandalhu, this interactive PDF addresses common points of confusion around air filters. Rebuttal Matrix for Advocates of Air Filtration in Schools Based on Common Barriers > Presenting v4.0 aka the "I can't believe we're still doing this in August 2022" version. > Additions: new concerns addressed, pdf with hotspot links to references. Interactive pdf link here: https://t.co/Rdup91LOMO https://t.co/PIUEDgkcxN pic.twitter.com/tFaLkPB6Qn > > — Amanda Hu (@amandalhu) August 22, 2022 * * * Find more tweets about this: Box fan filter #corsirosenthalbox #CorsiRosenthalBoxes #CorsiBox Corsi Rosenthal box * * * ## In the news: 3M scientists: This Corsi-Rosenthal box movement is legit Scientific American: We Need to Improve Indoor Air Quality: Here’s How and Why Upgrading buildings’ ventilation, filtration and other factors would not only decrease COVID transmission but also improve health and cognitive performance in general CBS News: New air purifiers filter at least 90% of COVID-carrying particles, researchers say WIRED: Could a Janky, Jury-Rigged Air Purifier Help Fight Covid-19? DIY Air Filters For Classrooms? Experts Are Enthusiastic — And A Citizen Scientist Makes It Easy Smithsonian Magazine: The Homemade Air Purifier That’s Been Saving Lives During the Covid-19 Pandemic. Made from everyday items found in hardware stores, the Corsi-Rosenthal box is a testament to the power of grassroots innovation UCSD students, staff build filtration boxes to prevent spread of COVID in classrooms NBC News: What to do if a family member tests positive? How to ‘Covid-proof’ your home. The best strategy for avoiding the Covid virus is to make indoor air as much like the outdoors as possible, experts say. Brown University: Students unite to take a hands-on, DIY approach to improving air quality. An event hosted by Brown’s School of Public Health brought students together to build low-cost, highly effective Corsi-Rosenthal cubes as air filters that will augment existing filtration systems at Brown. UCDavis: The Corsi-Rosenthal Box: DIY Box Fan Air Filter for COVID-19 and Wildfire Smoke

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