Why Air Filtration is Important to Stop the Spread of COVID-19

Written and Researched by Evan Wang (15), Certificate of Distinction by placing in the top 0.57% of more than 19,000 students (top 100 out of 19000) writing the Fermat Math contest globally.


As school comes back into session, there seems to not be much actionable advice. The advice that I have found is vague, like increasing ventilation. How much do you need to increase ventilation and how much safer will it make me? I along with many of my friends and family are concerned about the spread of COVID-19 in schools. I am not an expert but I am an incoming sophomore who has read a lot about what is going on and has done a bunch of research over the summer. All the math is based on publicly available information from institutions like the WHO and CDC.


Large groups, positivity, activity and how it affects risk

You should not hang out in large groups due to the greater possibility of someone being symptomatic or not symptomatic.

Depending on how serious of a case of COVID-19 a person has, they expel a certain quanta of virus particles. Quanta is a unit of measuring how many virus particles a person is expelling. This quanta affects how much risk you are at of contracting COVID-19. A person who is not doing much and is asymptomatic could release less than one quanta of virus particles while someone who is very sick would release 4-6 quantas. I am estimating the risk of contracting COVID-19 based on the new cases per million, but there is no way to know the exact numbers because people are getting infected all the time and test results often come back a week late.

By using this spreadsheet, you can calculate the projected number of spreaders and quanta in your area.

You can estimate the positivity rate at your school by using the local positivity rate data on this website.

Air Flow and how it affects risk

When someone contracts COVID-19 they slowly expel the virus from their lungs. According to a WHO study, you can reduce the chance of contracting Covid-19 to less than 1% by increasing the air flow to 12 air changes per hour(ACH) to take the Covid out of the air. I used the Wells-Riley Equation to estimate the risk based on the amount of ACH you have in the room.

According to both the CDC and WHO, you want to have at least 12 air changes per hour(ACH)

In order to use this spreadsheet you need to know how many people are in your room. What you are trying to do is project how many infections you should get depending on your air flow, number of people, what those people are doing, and how long they are in this enclosed space. These variables are important because if someone is exercising or yelling they would spread COVID-19 more easily. If someone was in a room for a long time they would be more at risk for contracting COVID-19.

You are probably wondering what your current ACH is? The ashrae standards specify how much outdoor air that you are required to have. I can’t say for sure if you are over or under the standards but this is a decent estimate.

How to estimate required CFM?

You want to add more ventilation. How do you determine how much? Cubic feet per minute (CFM) is used to measure the airflow in a room. You can estimate the required CFM based on how big your room is. Here is a calculator to help you estimate the ventilation required.

How to add CFM?

You can add CFM by increasing the ventilation but that is problematic because the ventilation unit can only vent so much. Just increasing the intensity on standard AC will just push the viruses around the building because it is not hospital grade filtering and there is little outside air. To filter viruses, you can add a MERV13 filter. However, unless you have hospital grade ventilation, you will burn out the AC. In my experiments, a MERV13 filter reduced the air flow by 4x. Weaker fans treated it like a wall.

I have a video that shows you how to add 600 CFM of hospital grade filtration to a room for only $30. HEPA fans work great too but they are much more expensive. My Dad said that he would have two on his desk if he was going back to the office. I also have a spreadsheet of a number of options that I have tested.

Link to video

My Proposed Solution

I have an idea using an inexpensive fan to improve the air flow in classrooms which in turn will help reduce the spread of COVID-19. Here is a list of 5 simple steps

Measure how big your room is.

You want to measure how big your room is because you need 12 air changes per hour and how much ventilation you need to reach 12 air changes per hour is dependent on how many cubic feet your room is.
Plug your room size into this spreadsheet to find out how much CFM you would need for your room and how much it would cost if you used our recommended fan and filter.
Decide what fan and filter you want to get
You want to make sure the filter is MERV-13 rated and is the same size as the fan.
If you don’t know which one to get just buy the one we have tested
Follow our video on how to create a filter fan
The video explains step by step how to build your own filter fan using easily accessible materials
Spread the fans out to get circular ventilation to effectively filter air


If you can’t get to 12 ACH, you can vent the room every hour or so to prevent the COVID-19 particles from building up in the room due to insufficient ventilation. If you have access to an outside window then venting the room using fans is ideal. It takes 20 minutes to cycle out 98% of the air in a room with 12 ACH. It would take an entire day to effectively kill COVID-19 in a room with humidity. However, between classes you could take the filters off the fans and vent at 60 ACH which would cycle out all the air between classes and make sure there is no cross contamination between groups.

Here is how you calculate how long it will take to properly vent a room with your fan power.

Venting is not always practical. For example, if it is 40 degrees below freezing or 100 above outside or if you have no outside window. In that case, you want to make sure that you have proper humidity and MERV13+filtering.

Pictures of Box Fan With MERV-13 Filter and Assembly Pictures


Charities and philanthropists can support this effort. Volunteers such as boy scouts, girl scouts and grade school children would be able to assemble the donated box fans and MERV-13 filters or buy those from donated funds.

One box fan and filter for each person starting with seniors and the most vulnerable would greatly reduce the risk of transmission.

These fan and filters can also be used at restaurants, businesses, offices and other locations.


You do not want to wear one way valve masks because they only filter the air coming in, but not out which endangers other people. Bandanas are no good either. Scientists at the Florida Atlantic University found that air travels 3 feet 7 inches when you cover your face with a bandana. If you compare that to 1.25 feet with a double-folded handkerchief it is clear that bandanas are not an effective way to prevent the spread of COVID-19.


Cleaning your mask

Peter Tsai, the inventor of the N95 mask, found that the best way to sterilize a used N95 mask is to put it in the oven at 160 degree dry heat for 30 minutes. However his preferred method is to buy 7 masks and rotate them every day for a week, so you could use a new one everyday. He hangs all the used ones in isolated spots for a week, so the bacteria becomes inactive.


Cleaning is important but not that effective

Practicing proper hygiene is very important, but deep cleansing all your surfaces frequently is overkill and is not an efficient use of your time. Most of the COVID particles that are dangerous are airborne and are not being killed by power washing all your furniture.


Good Luck and Stay Healthy!!!!

ACH – Air Changes per Hour – A measure of ventilation that is not dependent on room size.
CFM – Cubic Feet per Minute – a measure of ventilation that you multiply by 60 and divide by room volume to get ACH.
Quanta – A measure of virus particles being expelled in the room

List of Calculators
Air Changes per Hour by building type
Projected Infections by time and ACH
CFM Calculator

Additional Reading


10 thoughts on “Why Air Filtration is Important to Stop the Spread of COVID-19”

  1. This is not going to turn your house into a class 100 cleanroom. It will just lower the total microbe load.

    And yes, if you live is a highly filtered environment, 24/7/365 you are asking for trouble. For a couple of months I wouldn’t worry about it.

    If you are concerned, just make sure you go out and play in the mud every week or two. You do that anyway, right?

    I mean good, honest, rural mud, where you are more likely to encounter a dangerous animal than a diseased human.

  2. As Mindbreaker said, they have prefilters you can vacuum. The fan part themselves also are don’t last forever, so that part fails first. The thing with filters, is that the more stuff they filter out, the better they filter… It just becomes harder to pull air through them. So, I guess the lifetime thing is it part marketing. But the filters also have a lot of surface area, much more accordion like than the furnace types. Think a Honeywell 50250 or 17000. They used to call them permanent or lifetime filters, but I just noted they are now calling them “long life” filters.

  3. Is about 0.26% based on serology tests. Factor in TCell immunity and that value is effectively halved. So overall you’re looking at an IFR of about 0.13%, which is inline with a bad flu season.

    I will not stop posting this. It is important people realize they’ve been duped by mainstream media, politicians and other nefarious lots who only seek to continue profiting from our suffering.

    Nobody seems to be talking about Sweden these days. I wonder why?

  4. This is the thing that bothered me about opening the schools. There was no attempt to install HEPA filters in the classrooms. Reducing the number of virus particles in the air can reduce transmission and it can also reduce how severe the disease is.

  5. This is a nice article! Well-written, complete sentences, proper punctuation and grammar are present throughout. The premise, supporting information, and conclusion are clear. Well done. Brian, you might have Evan be your editor. 🙂

  6. But if we filter out all virus and bacteria from the air, do we make the environment to sterile? Don’t we need a “little dirt” to stay healthy, also in terms of virus and bacteria?

  7. a lifetime HEPA filter

    How does that work? If you are filtering out a lot of pollen and dust, you’ll build up a layer of crud on the filter and it’ll stop working.
    Is it a system that allows you to clean it the buildup away?

  8. The filter taped to the box fan in the box is pretty clever. I live in the deep south that has “pollen season”, a Honeywell air filter with a lifetime HEPA filter was a necessary buy the first few years I moved here. HVAC people told me it was better to have purpose built filtration rather than sticking the high efficiency filters in the furnace air handling units since it wouldn’t move the air well enough for the proper heat transfer efficiency. My concern with an office environment is that sure the filters will remove some things from the air, but you’re also circulating stuff more. So the viral loading may go down, but could be farther reaching. To answer if more filtration would be better for reducing COVID cases would require outcome research.

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