Clean Air vs COVID
COVID-19 is largely spread by respiratory particles in the air. Large droplets drop to the ground quickly but smaller particles (“aerosols”, roughly 0.3 to 3 micrometers) can stay in the air for hours. Fortunately there is a low cost method to remove these droplets using a simple box fan and filter. The goal is to get as much air through the filter as possible to increase your clean Air Changes per Hour (ACH). Click below to order a kit or donate one, or keep scrolling for all the info. Note – please do not substitute less expensive / effective filters as they do not work nearly as well for small particles that can carry COVID.
Some Links Contain Affiliate Information with Funds Going to Support Development of Educational Content
We want to ensure equal access for all teachers, students, and administrators. You can make a tax-deductible donation through Community Venture Foundation that allows us to order supplies at wholesale, optimize distribution, and maximize the impact of your support. We encourage teachers to fill out our Google Form to help us identify needs and distribute kits as effectively as possible.
Donations through Community Venture Foundation / Startup Junkie Foundation are Tax Deductible
Prefer Bitcoin? You can send to: 171zZK9sru9M5rVhrE52SMsytqFfiiWzmY
Prefer Ethereum? You can send to: 0x383A59dBFB949DE9D22324b8284f6f7D960f5bF6
In the most basic form you can attach a single filter to a box fan. However, Richard Corsi and Jim Rosenthal showed that building a cube greatly increases airflow (increases effectiveness) and reduces noise (increases usefulness). Read about the lab testing and results below. The construction is fairly simple, you can use the box from the fan to create the base, and then secure four MERV-13 filters to the sides, position the fan on top, and create a shroud to cover the corners of the fan to improve performance. You can find detailed instructions and a video guide will be coming soon. Note that you can encourage creativity by using any shapes or configurations, but the cube is what has worked best in our testing. The key is getting as much air through the filters as possible, without letting unfiltered air leak into the fan.
Be sure to orient the filters with the flow direction pointing in and place the fan so it blows upward, as indicated by the arrows on the right image above.
What You Need
There are many variations on the design but the basic components are the same. You need a fan, the filter(s), and something to seal them together.
Air filters are often categorized by their Minimum Efficiency Reporting Value (MERV) rating. This measurement scale was designed to compare the performance of filters across a range of particle sizes. The higher the rating the more effective a filter is at trapping smaller particles. A MERV 13 filter provides ~85% efficiency at trapping particles in the range of interest for COVID [Source].
Our recommendation: 3M Filtrete Advanced Allergen filter (20x20x1). While it is MERV 12, not 13, we think it’s a good price/performance balance (see data below).
Note: FilterBuy MERV13 filters removed 3x fewer particles in our tests.
Box Fans are fairly standard with a size around 20 inches by 20 inches. The most important thing for this project is that the size is a good match to the filters, and the power cord comes out of an edge (usually the bottom). While there is relatively little difference between models in the lower price range, they can vary in noise levels and aesthetic appeal.
A good seal between the fan and filter is required reduce “leakage” — unfiltered air that gets blown out by the fan — that reduces filter performance. The simplest approach is to use duct tape all around the edges of the fan/filter interface. The kits include a roll of white tape (the most visually neutral, or you could use your school’s colors) but we also have 3D printed clips that are available for you to download and print, plus weather stripping for the seal.
The fan/filter kits serve as an excellent educational resource in addition to reducing the spread of COVID. Having students explore different configurations with multiple filters, filter thicknesses, and overall geometries creates a way to integrate the kit into Mathematics, Science, Art, and English Language Arts. Working with teachers, we are developing a variety of lesson plans for elementary, middle, and high school, so please check back soon. We love giving students the chance to engage with their lessons as that is how we best learn ourselves. Check them out and feel encouraged to submit your own!
Filter Testing in Arkansas
These box fan filters are becoming increasingly popular in posts online, but we wanted to know if they really work. We tested their particle filtration efficiency using a 7-channel particle counter for particle sizes between 0.3 and 10 µm, and we used a flow capture hood to accurately measure clean air flow through the filter and fan combination. What we learned is that with the proper construction (sealing all holes and adding a shroud around the corners of the fan), the filter performance matches the manufacturers’ specifications and the flow rate is outstanding. While these filters extract particles less efficiently than HEPA filters, they more than make up for it with increased air flow. Because the “clean air delivery rate” is the flow rate times the particle removal efficiency, these DIY box fan filters offer performance that rivals or even exceeds similarly sized commercial HEPA filters.
Hugh Churchill, Ph.D. is a Quantum Physicist and professor at the University of Arkansas with a passion for using science to build a better world. Douglas Hutchings, Ph.D. is an entrepreneur and advocate for STEM education. We did not invent this idea, but these purifiers have been proven to be effective in a range of settings from helping families impacted by smoke from forest fires all the way to dealing with seasonal allergies. As COVID is rapidly spreading and schools are starting their semesters, we wanted to make sure that teachers, parents, students, and administrators know there are low-cost options that can make a difference, with filter performance tested by researchers in Arkansas. Learn more about this effort in the video below.
Expand Options with 3D Printing
There are tons of educational opportunities with these kits and you can incorporate 3D printing if available. We made custom clips that you can print and use with your own setup. They work well to help reduce leakage but tape works as good (or better) in many cases so don’t feel like you NEED a 3D printer. How would you change them to improve performance?
Buy Kits Direct
If you want to get started right away, then you can simply buy all the pieces you need right now. You can buy all the parts from your favorite retailer and simply use tape or another method to attach the fans and filters.
If you want to help even more, you are able to make a tax-deductible donation through the Community Venture Foundation / Startup Junkie Foundation. We will use your donation to provide kits to teachers and administrators in Arkansas. We will use our list of pre-identified teachers coupled with feedback from state and local leaders to deploy them to those most in need. One kit can clean the air in most classrooms or bathrooms, and additional kits can be used to help in band rooms, gyms, or the cafeteria.
“We have almost no information about a lot of technologies that are being heavily marketed to school districts right now. They haven’t been rigorously tested and reviewed in peer-reviewed literature,” he said. “There’s lots of reasons to be skeptical of their ability to be effective.”
But with this DIY device, Corsi said, “We have a real winner.” – Source
“Low-cost portable air purifiers, similar to those used in our testing, are impactful at improving indoor air quality when appropriately matched to a room’s size. This is particularly important for shared spaces in older buildings where ventilating with clean outdoor air or making substantial improvements to HVAC systems is not an option. Portable air purifiers may be beneficial as one component of a layered approach of precautions, such as distancing, handwashing and mask-wearing, to protect individuals from respiratory virus transmission.” – Dr. Meng Kong, research scientist, Well Living Lab – Source
Want to Get Involved?
We need your help and there are many ways to get involved. We need help to deploy kits and raising awareness. In partnership with Startup Junkie Foundation we are able to received tax-deductible donations that enable us to do bulk purchases and distribution. This website will be continually updated with new educational content and we welcome expertise in web development and social media management. Ultimately a simple share with your network is greatly appreciated as we work towards equal access for all teachers.
Terms and Rules Agreement – I.e. The Lawyers Made us Say It
By making use of any information on this website, you agree to the following:
NO WARRANTIES: All of the information provided on this website is provided “AS-IS” and with NO WARRANTIES. No express or implied warranties of any type are made with respect to the information, or any use of the information, on this site. CleanARAir and the authors/contributors make no representations and extends no warranties of any type as to the accuracy or completeness of any information or content on this website.
DISCLAIMER OF LIABILITY: CleanARAir and the authors/contributors specifically DISCLAIMS LIABILITY FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES and assumes no responsibility or liability for any loss or damage suffered by any person as a result of the use or misuse of any of the information or content on this website. CleanARAir and the authors/contributors assumes or undertakes NO LIABILITY for any loss or damage suffered as a result of the use, misuse or reliance on the information and content on this website.
USE AT YOUR OWN RISK: This website is for informational purposes only. It is your responsibility to independently determine whether to perform, use or adapt any of the information or content on this website. Any DIY of any sorts may result in injury. By undertaking any of the projects or builds displayed on this website, you assume the risk of any and all resulting injury.
Be safe out there!