FOR IMMEDIATE RELEASE
January 22, 2025
Media Contact: James Doernberg, press@corsirosenthalfoundation.org | 434-218-0709
1000+ Air Filters Delivered to LA Wildfire Survivors
Grassroots Volunteers use DIY Corsi Rosenthal Filters for Disaster Rapid Response
(Los Angeles, Ca.) — As wildfires engulf large areas of Los Angeles, harmful particles and toxic gases from the wildfire smoke pose major respiratory health risks to Los Angeles residents. For Liesl McConchie, a board member of the Corsi-Rosenthal Foundation and a San Diego resident, the fires and respiratory dangers were literally close to home, and she knew that rapid deployment of air filters would protect the health of thousands of at-risk Angelenos. McConchie and her Foundation colleagues quickly designed a rapid response initiative to build and distribute DIY Corsi-Rosenthal air filters. In the last two weeks, the Foundation has built 1,150 air filters using $30,000 in supplies and 1,000 MERV13 furnace filters donated by 3M, and raised almost $10,000 from the public through a campaign on its website: https://corsirosenthalfoundation.org/donate/
DIY filters can be built cheaply and quickly from materials readily stocked by any hardware store (box fans, MERV13 furnace filters, and duct tape), and the EPA recommends them as “a cost-effective approach to improving indoor air quality during wildfire smoke events.”
Over two weekends, McConchie converted her San Diego backyard into a makeshift assembly line and enlisted her husband, her kids, and 60 San Diego volunteers to assemble 650 air filters bound for LA. “The last two weeks have been a total whirlwind,” said McConchie. “My house became a small factory, my kids helped me pack a 20-foot box truck to the brim, and I drove a truck around LA dropping off supplies to amazing people protecting their community. Working with these selfless volunteers and the wonderful community groups from hard-hit LA neighborhoods has been an exhausting but so rewarding experience; it’s been truly inspiring seeing so many people come together to help in this emergency.”
In parallel, the Foundation supported Joaquín Beltrán, an advocate with the LA-based Action, Care, Equity Coalition, by donating materials to build another 500 air filters. Beltrán set up his own volunteer production line run out of a car dealership that provided space.
Through McConchie’s and Beltrán’s efforts, more than 1,150 air filters were assembled and distributed to emergency shelters, senior care facilities, schools, neighborhood associations, and vulnerable community members, all in the span of 12 days.
The Corsi-Rosenthal Foundation, founded by Indoor environmental engineer Dr. Rich Corsi and air filter expert and manufacturer Jim Rosenthal, will continue contributing to the wildfire response, but focuses most of its grants program on providing air filters to schools, furthering public health by reducing students’ and teachers’ exposure to viruses, allergens, and other harmful airborne particles.
“We’re glad that we were able to provide so many air filters to areas heavily impacted by wildfire in Los Angeles,” said Jim Rosenthal, the Foundation’s President. “In addition to providing these filters in this moment of crisis, we also want people to understand that cleaning indoor air is important, it has a direct connection to health, and affordable and effective solutions like Corsi-Rosenthal Boxes exist.”
A video and some photos from the wildfire response are available in the Foundation’s LA Wildfire Response Media folder.
About the Corsi-Rosenthal Foundation: The Corsi-Rosenthal Foundation is a 501(c)(3) nonprofit Corporation whose mission is to improve human health by supplying and promoting the use of air filters to clean indoor air. For more information visit: https://corsirosenthalfoundation.org/about/
3M has made a substantial donation of Filtrete™ Air Filters valued at over $100,000 to the Corsi-Rosenthal Foundation and their CleanAirK12.com initiative to build Corsi-Rosenthal Boxes for schools and community centers.
The Corsi-Rosenthal Foundation began as a global grassroots movement to build a low cost, open-source do-it-yourself (DIY) air purifier in response to the COVID-19 pandemic. The DIY air purifier, known as the Corsi-Rosenthal Box, can be constructed in less than 45 minutes with simple materials costing about $60 to $100: air filters, duct tape, and a box fan. The Corsi-Rosenthal Foundation also operates the website CleanAirK12.com, an initiative of the CR Foundation aimed at expanding the reach of the Corsi-Rosenthal Box by offering free box kits and educational resources designed for classrooms.
Humans spend up to 90% of our time indoors. Indoor spaces can be poorly ventilated, and the COVID-19 pandemic highlighted the importance of clean air. Indoor air can also be contaminated with allergens, pollutants and particulates.
Air purifiers are an effective way to clean indoor air of airborne particles, but often those most in need of air purifiers are least able to pay for them. The Corsi-Rosenthal Foundation provides grants, resources, and information so people and organizations can build their own air purifiers. The Corsi-Rosenthal Box has been tested against some of the most stringent air purifier standards in the world using ISO certified equipment by experts in aerosol science and public health (including from 3M scientists!) demonstrating effectiveness. This means those who need an inexpensive, powerful air purifier can build one themselves, using locally sourced components for a fraction of the price of a commercially manufactured air purifier. The Corsi-Rosenthal Foundation estimates over 200,000 Corsi-Rosenthal Boxes have been built by a global audience of clean air enthusiasts—many of whom share their creative designs on X (formerly known as Twitter).
The federal government found that over 41% of U.S. school districts need to update or replace HVAC systems in at least half their schools. The Corsi-Rosenthal Foundation understands that lasting change requires more than just innovative technology; it necessitates community engagement and education. To this end, they launched CleanAirK12.com to support classrooms and educational organizations, raising awareness about the importance of clean air and providing a STEM project centered around building a Corsi-Rosenthal Box for the classroom. Specifically, through CleanAirK12.com, schools can apply to receive a FREE kit of materials to build a Corsi-Rosenthal Box—the donated Filtrete™ Air Filters will be among the inventory leveraged to support these donations. Applicants will be prioritized based on three criteria: 1) need and capacity of organization; 2) quantity and capacity to deliver; 3) strategic partnership value for scale. Other nonprofit organizations are also eligible to apply for the free kit materials and are encouraged to apply directly through the Corsi-Rosenthal Foundation website. To date, between CleanAirK12 and the Corsi-Rosenthal Foundation platforms, the Corsi-Rosenthal Foundation has donated the materials for 500 Corsi-Rosenthal Boxes across 18 grant partners.
“Corsi-Rosenthal Foundation is still in its embryonic stages” said Foundation President Jim Rosenthal. “At this point, we are 100% volunteer and largely self-funded. That is why the 3M donation is so important to us. This generous donation of Filtrete™ Air Filters from 3M moves the Corsi-Rosenthal Foundation to another level, nearly doubling our capacity to serve our partners.”
Learn more about how to apply for air purifier kits or how to support this organization with a donation by visiting this link.
From the early days of the COVID pandemic, Corsi-Rosenthal (CR) boxes thrust filtration into the spotlight of indoor air quality (IAQ).
While all high-efficiency filtration lowers viral load by mechanically removing airborne particulates, these DIY boxes popularized high-performance filtration with affordable, easy-to-source materials (furnace filters and a box fan).
In commercial settings, the primary metric for filtration performance is efficiency. Specifically, first-pass efficiency: the percentage of particles of a specific size range that are removed with one pass through the filter.
This focus on efficiency is why HEPA filters have been the gold standard in the IAQ industry.
It’s an easy pitch for a sales team: Our filter is lab-tested to remove 99.97% of particles, including COVID!
The problem is that a cheap CR box significantly outperforms many HEPA filters in real-world tests.
What! How? Why!
Because focusing on efficiency misses half of the equation. Clean air delivery rate (CADR) is what really matters: that’s efficiency times airflow.
Wha- why does airflow matter?
Because a filter only cleans air that physically moves through it. Higher airflow means a unit processes more air per hour.
It’s like a kid and an adult stealing from a cookie jar. Sure, the adult can hold more cookies in one hand, but those kid hands are relentless— the kid grabs one cookie at a time but they do it again, and again, and again.
HEPA is the adult. A high removal rate but they don’t reach into the jar as often.
Note to new parents: this is why we put the cookie jar out of reach.
No. Well, maybe. Sometimes.
CR boxes are a DIY solution that’s affordable and accessible. They’re great for spot filtration during periodic, high-risk events like wildfire smoke, sick family members, creating in-house isolation rooms, etc.
They’re cheap and effective.
But they’re also large, noisy, and inconvenient– those drawbacks are manageable for short periods but deal breakers for a long-term solution in a commercial space.
One of the lasting legacies of the COVID pandemic will be the public’s interest in IAQ. We’re at the edge of a paradigm shift in realizing the importance of clean air in our communities. A similar shift happened when cholera and other waterborne diseases changed how we test, monitor, and treat water.
Improving water quality was required for public health.
We need to think the same way about clean air.
But to provide clean air at scale, we need affordable products with standardized, replaceable parts with low noise, high CADR, and good designs to operate conveniently in different spaces.
We need C.L.E.A.N. filters.
I see what you did there. Clean air. Cute.
Components, Location, Efficiency, Airflow, and Noise.
That’s the measure of a good filter.
Most standalone HEPA filters excel in one category. The original CR boxes are competent in three.
High-end residential HVAC covers all five but low-end systems barely do one.
Listen, I love acronyms as much as the next person, but what does it *mean*?
At its most basic, filtration is simply airflow through a filter to remove particles. That covers a range from CR boxes to engineered HEPA systems.
All of those filters have four (4) key components: frame, electronics, fans, and the media filter. Each component varies from proprietary and custom to open-source and off-the-shelf.
CR boxes are popular because the components fall into the latter category. Every part is available at your local hardware store.
Proprietary and custom parts are better, right? RIGHT?
For the filter company, yes. It ties consumers to one company for higher ongoing costs with expensive replacement filters and repairs.
It’s a captive market.
The antithesis is the residential furnace filter market with standard sizing and competition driven by the consumer’s ability to switch brands.
Commercial filter replacements can be 10 times more expensive than residential filters.
The ideal filter uses commodity components with replaceable parts and residential furnace filters to reduce costs while maintaining performance.
Schools have different use patterns and requirements than houses, small businesses, or medical treatment rooms.
CR boxes are good options in houses because noise levels and floor space aren’t as valuable. Many homes have central HVAC systems that easily handle the filtration requirements for low occupancy.
Schools are high-occupancy spaces with lots of traffic, limited floor space, and less patience for noise.
The physical placement in a room is also important.
Ah, so what is the best place for a standalone filter?
That’s easy– it’s the place that doesn’t interrupt anyone in any way.
See, a partially obstructed or poorly placed filter has a reduced CADR or creates dead zones with poor distribution of clean air in the room.
But that’s nothing compared to inconvenience. An inconvenient filter gets unplugged, and an unplugged filter has a CADR of zero.
This is the “hot take” section but I feel a sense of conviction because of research by Jim Rosenthal, David Elfstrom, and Joey Fox.
The industry holds first-pass efficiency as the gold standard for filter performance.
But that wisdom is wrong.
And it leads to the wrong solutions.
The removal rate of particles (i.e. the underlying goal of filtration) is driven by CADR not efficiency.
So do all HEPA filters have bad CADR?
Not at all! Hospitals and operating rooms with high-risk, contagious diseases use engineered HEPA systems to achieve 99.99% first-pass efficiency with high airflows.
HEPA filters are also great solutions in vacuum cleaners, powered air-purifying respirators, and extreme conditions like capturing radioactive particles from research lab exhausts.
But a standalone HEPA filter with low airflow has poor CADR and underwhelming performance because it doesn’t process enough air.
I’m convinced. It sounds like we shouldn’t care about efficiency at all.
Intuitively we understand the need to stay above a minimum efficiency threshold; a lonesome box fan doesn’t clean the air. After all, CADR equals efficiency times airflow so we need a non-zero removal rate to make it work.
I get it, a baby doesn’t steal any cookies from the cookie jar.
MERV-11 is the lower limit. Below that, a filter has minimal ability to catch respiratory particles. I mentioned low-end HVAC systems earlier: a standard furnace includes a MERV-8 filter. For our purposes, that’s a CADR of zero.
The other side of the CADR equation is airflow. Airflow is easy to increase but needs to be balanced with noise levels.
Standalone HEPA filters are plagued by noisy operation. They usually have three or more fan speeds and the performance is tested on the highest speed. That produces a great CADR for marketing brochures but it doesn’t reflect real-world performance.
Does airflow really matter as much as efficiency?
Totally. And it’s easier to hit.
Tests from Jim Rosenthal show that MERV-13 with higher airflow significantly outperforms HEPA filters.
The downside to airflow is noise.
The best-case scenario for a noisy filter is getting switched to a lower fan speed. The worst-case is getting turned off or unplugged.
In the fight between noise and airflow, consumers choose quiet operation over performance.
Indoor environmental quality (IEQ) wins because the annoyance (noise) has an actionable fix with immediate satisfaction. That easily beats the invisible benefits of IAQ.
Filters get tested for noise, don’t they?
Yes, but the results are a range based on the different fan speeds and marketing materials focus on the lowest speed for noise levels.
Filters need to be tested for CADR and noise at the fan speed that’s used in the field (the lowest speed).
The burgeoning community science market for CR box development gave us a brilliant solution: PC fans.
PC fans are performance-optimized, quiet, commoditized, and single-speed.
Check, check, check, and check.
We need to adjust our lens for high-quality filters, shifting from efficiency to effectiveness.
But, aren’t those the same thing?
Efficiency is a single variable. Effectiveness reflects the full scope of the CLEAN framework that’s rooted in real-world performance, occupant behaviours, and accessibility.
An effective filtration system uses replaceable components with affordable filters to ensure constant air cleaning with dependable results. It’s a system with low noise and high CADR that operates in various settings without disrupting occupants.
We’ve been focusing on the wrong metric for healthier buildings.
Particulate filtration happens one way or another. Either communities, companies, and individuals invest in effective solutions or that role falls to our lungs.
On average, we spend 90% of our time indoors.
Imagine that. When you turn 40, you’ve spent a combined 36 years in buildings.
And now consider the compounding benefits of fewer sick days, lower absenteeism, and increased productivity from cleaner air. School boards, businesses, and countries that prioritize clean air will see world-changing benefits over time.
The next time you’re buying or recommending an air filter, make sure it’s CLEAN so we can take definitive steps toward cleaner air and healthier people.
We’ve all heard it before. Surely you can’t stop a virus with a filter because the gaps in the filter are too big and something as small as a virus would just pass through?
Well hold on!
It’s not that simple!
EPA (Efficient Particle Air Filter) and HEPA (Highly Efficient Particle Air Filter) really do capture tiny particles as small as viruses with incredible efficiency. Even though the gaps in them are much bigger than they are.
In fact – (fun fact) – the smaller the particle is, the better these filters are at capturing it.
Yes…. Really. You read that correctly. EPA and HEPA filters capture tiny nano particles more efficiently than, say, mere microscopic particles even though these are much, much smaller than the gaps in the filter itself.
It sounds counterintuitive, but these filters make use of a couple of bits of funky physics to achieve this. Here’s an explanation with, of course, an angle related to our unwelcome guest the Coronavirus…..
A Coronavirus particle is approximately 0.12 microns in diameter, and that is absolutely tiny. In fact, it’s been calculated that all the Coronavirus in the world wouldn’t fill a coke can.
It’s small. Really, really small, but….
Viruses and Germs don’t travel alone. They travel in aerosols which all of us breathe out. The WHO defines an aerosol as anything which can remain suspended in the air including dust or fungal spores. While there’s some debate about the physical definition of an aerosol a particle of 5 microns or smaller has usually been used as the benchmark. That’s bigger than a virus, but still minute and much smaller than the gaps in a filter, so what else does a filter have up its sleeve?
Firstly, filters are pleated to ensure that their available surface area for filtration is enormous in relation to their size. We don’t necessarily advise you to do this (in fact we’ve done it so you don’t have to), but if you were to unpleat a standard 12 x 20 HEPA filter you would be left with a strip of material that was approximately 9m or 30ft long. (Don’t do it. Just don’t.…)
This is a principle with analogies in nature. Your lungs and your intestines are far more effective at absorbing tiny oxygen and nutrient particles than a simple measurement of their size suggests they should be. This is because their surfaces are packed with “pleats” called alveoli (in your lungs) and villi (in your intestines) which massively increase their surface area.
The filter’s enormous surface area means a tiny particle has to pass through a lot more filter material than it would if the filter were unpleated, drastically increasing the chances that it will be trapped.
Secondly, unlike normal fabric, the fibres which make up a filter are packed together irregularly. This means that there is no neat, straight gap in a filter that a particle can travel through. If you want to picture it, think of a particle navigating an obstacle course, blocked by fibres at every turn.
Moreover, the outsized (very large) surface area surface area of the filter means a particle has to effectively pass through several obstacle courses without being trapped before it can find freedom on the other side. Hopefully you’re already forming a picture of why this is becoming unlikely!
This is the final trick, and also explains why filters become more efficient at trapping particles the smaller they are.
When air is passed through a filter, the air molecules knock the very tiny particles in it around randomly. This phenomenon is known as Brownian Diffusion, and means that small particles pinball around as they move. Even if you had a straight gap through a filter, small particles would be more likely to hit the sides of it than to pass straight through it.
This is where the final trick comes in. The fibres which make up the filter are made “sticky,” with a long lasting electrostatic charge that holds particles.
Have you ever rubbed a regular party balloon on a carpet and then watched in awe as your hair stands up when you pass it over your head? If not, try it.
Rubbing the balloon on the carpet has given it an electrostatic charge, and this attracts your hair.
Electrostatically charged fibres do the exact same thing to tiny particles. Random, Brownian movement makes tiny particles more likely to hit a fibre. As soon as they do they are captured and held fast by its electrostatic charge.
It’s game over.
The huge surface area of the filter, its random weave of electrostatically charged fibres and the random way small particles move make it almost impenetrable. Even to tiny viruses and the aerosols which carry them.
Almost impenetrable…. Of course some get through. That’s how randomness works, but here are some figures which show you just how good this is.
An E11 EPA Filter captures 95% of particles measuring 0.3 microns in diameter in air which passes through it, while an H13 HEPA Filter captures 99.97% of particles of the same size. A Study by NASA showed they’re even more efficient at capturing smaller particles (remember, Brownian Diffusion).
So all in all an Air Purifier with an EPA or HEPA filter is going to remove practically all the tiny particles, including virus and germ containing aerosols that pass through it. Even though the gaps in the filter are much bigger than the particles.
Layered protection is a concept borrowed from nature and replicated by humans as a design philosophy to minimise the risk of adverse events.
You may have heard of systems or things described as failsafe, resilient or redundant.
Our world has been revolutionised by being able to do things which are inherently dangerous because engineers have made things failsafe, resilient or redundant using layered protection. Read on for an example….
You probably take flying on a plane for granted. It’s fair to assume you will take off and land at your destination intact, uninjured and alive a few hours later ready to enjoy your holiday or your business trip.
How can you assume this? Flying is a perfect example of something which is inherently dangerous after all.
Flying has been made incredibly safe through the application of layered protection.
Every critical system on an aeroplane is replicated often multiple times, so that if a primary system fails a backup can take over. Often the backup uses different technology from the primary system, to limit the extent to which a single vulnerability can cause a critical failure.
From pilot checklists to triplicated computer systems, safe flying represents layered protection at its most optimised. As a result we can travel from place to place at velocities approaching the speed of sound in incredible safety.
Probably…..!
Layered protection is found throughout nature. You don’t need to look far to find examples either. Just look at your own body.
How many kidneys do you have? How about lungs? And even if the answer is “1” this still proves the point!…. Layered protection is everywhere in nature, and that’s because it works really, really well.
Living with Covid is, in our view, a great example of something which should be managed with layered protection.
Covid is inherently dangerous, with the potential to cause death and disability. While post-vaccination most people who get it will suffer milder disease, there is a risk of adverse and long-term effects, such as Long Covid. In addition, there is increasing evidence that absenteeism due to Covid and its potential effects is beginning to harm businesses, services and infrastructure – including schools and other educational settings.
The risks it poses are both individual and systemic and are significant.
When you travel on an aeroplane you don’t notice all of the layered protection in place which make 40,000ft in the sky one of the safest places to be.
It’s unintrusive.
Protections which are inconvenient or require lots of compliance are less likely to be sustainable in the longer term – against a threat which, if we do our job correctly, will be diminished but which could keep coming back.
This is why we think clean air in shared spaces is going to be a critical layer in our protections from this disease. The air can be replenished and cleaned without people noticing, and without them doing anything to make it happen. In fact, clean air has so many benefits besides infection control that if people do notice it, it’s likely to be for positive reasons such as their allergies being less intense!
The Coronavirus is an airborne virus.
In poorly ventilated indoor spaces we all share air, and this unfortunately is also how we share many common viruses and germs including the Coronavirus.
The virus is spread by hitching a lift on tiny particles called aerosols which are coughed, sneezed or simply breathed out by someone who is infected. These aerosols are so small that they can float in the air for hours, creating an infection risk for anyone who breathes them in.
So how can air purifiers help?
Outdoors, airborne transmission of viruses and germs is much less of a problem than indoors. This is because wind quickly disperses the aerosols they use to hitch a lift, while strong sunlight degrades the viruses and germs in them.
Indoors is a different story. In poorly ventilated indoor spaces, aerosols can accumulate and remain infectious for hours.
It is in these poorly ventilated indoor spaces that air purifiers can really help by sucking or blowing the contaminated air through a filter which traps almost all of the aerosols.
In this way it is possible to clean aerosols out of the air, reducing the risk that they spread infection.
Ultimately our aim is to make indoor air as covid-safe as outdoor air, using this and other technologies.
There are 2 things scientists consider when rating an air purifier.
The first is how efficiently its filter traps the aerosols, and the second is how often the air is passed through its filter.
Imagine a room with 1,000 aerosol particles floating in the air. Once all of the air in the room has passed through the filter once, then 95% of the aerosol particles have been removed. This leaves only 50 aerosol particles. The second time the air is passed through the filter, another 95% of particles are removed, leaving only 2 or 3 in the air. You can see from this that it is very important both to filter the air efficiently on each pass through the filter, and also to ensure that all the air in the room passes through the filter as many times as possible.
Together, the efficiency of the filter and the number of times air is passed through it in an hour make up the Clean Air Delivery Rate (or CADR) of the air purifier, usually expressed in m3/h.
Studies on ventilation have shown that completely replenishing indoor air 6 times per hour reduces Covid transmission by 82%.
As a guideline, if you are aiming to replenish the air in a room 6 times per hour and have no external ventilation, then calculate the volume of your room by multiplying its length by width by height (L x W x H) in metres. Then multiply this figure by 6. This is the minimal CADR in metres squared (m3) you would need to achieve 6 air changes per hour, or ACH. If you do have some ventilation and know how many air changes this gives you, then this can be added to your number of air changes. As a general rule it is better to have an air purifier that is too big than too small, and as many air changes per hour as you can cost effectively achieve!
Take a look at our calculator to help you decide (Link to Stefan’s calculator)
Evidence that air purification can work versus Covid is being gathered all the time, but the best evidence is simple physics. Air purifiers can remove almost all the aerosols from the air which the virus uses to spread. If it is filtered out of the air, then it cannot spread.
It is likely that the effect of air purification is greatest on far field transmission. This is transmission that happens over longer distances. We’ve all heard about cases of Coronavirus infecting people in offices, on cruise ships or at restaurants who had no close contact with each other. This is far field transmission.
See our Resources for studies showing how filtration can reduce the amount of Coronavirus (and other viruses and germs) in the air, and how ventilation, a close proxy for filtration, can reduce transmission:
Air purification is a risk reduction measure. Although we believe it can help a lot, it is one layer in the several layers of protection we should use. Layers of risk reduction are the best way to protect yourself, your family, your staff or your business.
As well as using air purifiers please also get vaccinated, ensure spaces you operate are as well ventilated as possible and adopt and encourage good mask wearing and hygiene practices.
Covid is not going to be easy to live with, but if we are sensible we can reduce its impact on our lives by reducing its transmission. Air purification can be a major tool in achieving this.
The Corsi-Rosenthal Foundation is a Not for Profit Corporation in the US and in the process of registering as a Charity in the UK.
Our mission is to improve human health by supplying and promoting the use of air purifiers to clean indoor air.
Humans spend up to 90% of our time indoors.
Indoor spaces are often poorly ventilated and the COVID-19 pandemic highlighted the importance of clean air in preventing the spread of viruses and other pathogens that can cause disease.
Airborne pathogens are not the only problem. Indoor air can be contaminated with allergens, pollutants and particulates which can cause acute and chronic illness, absenteeism and reduced quality of life.
Air purifiers are the best way to clean indoor air of airborne threats to our health, but often those most in need of air purifiers are least able to pay for them.
The Corsi-Rosenthal Foundation works to ensure the most vulnerable in society can enjoy the benefits of clean indoor air.
We fulfil our mission in two main ways.
We recommend or supply an air purifier to those most in need, either free of charge or with a voluntary donation that helps cover our costs. Those most in need include schools, healthcare settings and clinically extremely vulnerable people.
We also provide open source information including build instructions and kit lists, so people and organizations can build their own air purifiers. Corsi-Rosenthal boxes are the award-winning DIY air purifier named after our founders. This means those who need an inexpensive, powerful air purifier can build one themselves, using locally sourced components for a fraction of the price of a commercially manufactured air purifier.
In addition to this, we provide a general educational resource about air purification, infection control, and research through our website and network of expert professionals.
The Corsi-Rosenthal Foundation began as a global grassroots movement to build a low cost, open source DIY air purifier in response to the COVID-19 pandemic.
The DIY air purifier, known as the Corsi-Rosenthal box, is named after Dr Richard Corsi, Dean of the School of Engineering at UC Davis, and Jim Rosenthal, owner of a filter manufacturer and distributer.
The beauty of the Corsi-Rosenthal box is that from inception it was designed to be completely open source, built from different components which builders could select on the basis of price or local availability while still arriving at a consistent end product air purifier with a CADR (clean air delivery rate) of around 1000m3/h and a cost between $70 - 150. This is a phenomenal rate of clean air exchange, as many more expensive commercial purifiers have rates between 200-400 CADR.
This approach made the Corsi-Rosenthal box an immediate hit. It has become widely used in schools in the US, winning awards and attracting the attention of the White House, where, we are pleased to say, you will find Corsi-Rosenthal boxes in use.
Building a Corsi-Rosenthal box isn’t just a cost-effective step towards cleaner indoor air, it’s also fun!
Being open source allows people to get creative, and very quickly a global network of people optimising, improving and sharing their Corsi-Rosenthal boxes on social media started to drive adoption and improvement of the original design.
This network included everyone from members of the lay public following existing designs closely to expert engineers trying to improve or reiterate the original with their own innovations.
The Corsi-Rosenthal box isn’t just a nice idea. It has actually been tested against some of the most stringent air purifier standards in the world using ISO certified equipment by experts in aerosol science and public health. This is how we know the original Corsi-Rosenthal box easily holds its own against some of the most powerful and expensive commercial air purifiers on the market at a fraction of the price.
