The $33 Box Fan Filter for COVID-19

Yes, with a box fan and the right filter, you CAN eradicate the SARS-CoV-2 virus from the air to a very high degree. This is perfect for your average classroom, not to mention smaller offices and the home where a loved one may be battling COVID-19.

I fully understand teachers not wanting to risk getting COVID-19. But I also understand masks and filtration at the epidemiological, bacteriological, virological, molecular and atomic levels. Put simply, if the virus is the size of a mosquito and the filtration gap is the size of chain link fence, then the size of the mucous globules in which the virus travels range between a baseball and the entire baseball diamond.

Masks WORK, people. If you still believe otherwise, I strongly suggest you reverse your ignorance.

Even so, when you have 30 people sitting in a classroom, you will get an accumulation of mask leakage resulting in SARS-CoV-2 viruses leaking into the air. Over time, that could result in a high enough concentration to surpass the minimum required to contract the disease.

We know that the likelihood of virus transmission increases with duration and frequency of exposure of an uninfected individual with someone infected with the virus.

Skinner, M., Dr. (March 24, 2020). Expert reaction to questions about COVID-19 and viral load. Science Media Centre. Retrieved from:

Fortunately, there’s a cheap and effective solution.

For around $33 per classroom, schools can install a box fan-powered HEPA filter rated at the following levels (any higher and you’ll need a pressure pump to pass air through it):

  • MERV 13
  • MPR 1500-1900
  • FPR 10

Yes, both kids and teachers will STILL have to wear masks. The HEPA filter at an FPR 10 rating costs $18 and WILL remove viruses. Here’s a chart showing the average particle size efficiency for each MERV level. box fan costs $19, but you can buy them in bulk for $10 each. Add 160 inches (14 feet) of packing tape for $0.18 and you’ve got yourself a highly effective filter for removing the SARS-CoV-2 virus that causes COVID-19.

Run it on LOW, both due to noise and to minimize potential for overheating of the motor. Running it on high only doubles the throughput, but requires four times more electricity.

In 52.75 minutes, on low (quiet for classrooms), it still filters 93.8% of the air in the typical 30’x20’x10′ classroom. You achieve > 95% filtration ever 90 minutes. By the end of a typical school day, 99.2% of the air has been filtered.

I strongly advise adding a simple dust filter for less than $2 to extend the life of the HEPA filters. Tape is extra, but any packing tape will do.

  • Box Fan: $10
  • HEPA Filter: $20
  • Dust Filter: $2
  • Tape: $1
  • —————————
  • TOTAL COST: $33
  • ===============

Here’s what this looks like:

Alternatively, if you want to go with an inexpensive model that may do a better job of distributing the filtered air throughout the room, consider this, but reverse the fan so that it’s pointed up, not only for better clean air distribution around the room, but also to filter the more viral-dense air near the floor while keeping the fact and motor far more clean and free of dust.

And now, for the news…

President Biden received more contributions from teachers unions than any other candidate during the 2020 election cycle by a wide margin — underscoring the conundrum that may be headed for the White House if those same unions continue to oppose efforts to open schools for in-person learning.

Biden’s campaign raked in just over $232,000 from teachers unions during the 2020 election cycle, according to the Center for Responsive Politics’ “Open Secrets” website.

Olson, T. (February 5, 2021). Biden received more money from teachers unions than any other candidate in 2020. Fox News. Retrieved from: