What you’re looking at above is the end result of using a type of Corsi Box, as described in Post #854. That’s a fancy term for a cheap box fan with an HVAC air filter (or filters) attached.
Hence the circle of schmutz, on the air filter above, mirroring the circular blade of the box fan.
That filter has been running in the simple setup pictured below for a few months now. That’s a Filtrete ™ filter literally sitting behind a cheap 20″ box fan, held in place by the slight suction created by the fan on its lowest setting.
At the very least, I can now guarantee that this setup won’t burn out the fan motor. Not in any short period of time. Based on the dates on the photos, I’m just about at the three-month anniversary for this filter.
An actual Corsi box is constructed using cheaper (but higher resistance) high-MERV-rated filters. Corsi recommended using five, literally set up as a box, with the fan as the sixth side of the box. Instead, I did the obvious thing and used a single high-end 3M Filtrete ™ filter. It gives good filtration of aerosol-sized particles and has low resistance to air flow, but is fairly expensive.
(You can find discussion of all the common filtration standards in Post #593, which walks through all MERV, MPR, N95, HEPA, and other common filtration standards for air filters, masks, and other air filtration devices.)
And as you can see, this is about as minimal-effort as it gets. Unwrap the filter, sit it behind the fan, and turn the fan on low. It works even though the filter is actually sitting backwards on the fan (because I didn’t feel like tearing off the yellow filter timer on the back of the filter).
The idea of using cheap box fans and filters keeps popping up as a way to make indoor spaces safer. As outlined in Post #810. There’s no way to know if this will ever catch on, in part because nobody is going to test this, in any realistic way, as a way to prevent indoor spread of COVID-19. So even if you use setups like this, as suggested in Post #810, you can’t legally advertise that it reduces COVID-19 risk, because there’s no direct proof that it does.
Separately, based on what has gone on in (say) South Dakota, a lot of important people still can’t quite get their mind around the idea that things they can’t see can harm them. The idea that seemingly clean-looking air might be filled with tiny little particles that can hurt you. I guess that’s a bit of a stretch even for those of us who accept the germ theory of disease.
And if you don’t grasp that simple fact, then the idea of filtering the air that you breathe makes no sense. But what is a mask, if not a crude and portable version of the filter above. In my case, the mask is literally made out of the same material used in that air filter pictured above (Post #780, Post #807).
So a lot of people don’t quite seem to get it. But the schmutz does not lie. Even though I can’t see it, and the air looks perfectly clean, all of that came out of the air in my home. In any urban area, air that looks completely harmless is laden with particulates. It’s really no big stretch to go from aerosol particulates from diesel vehicles to aerosol emissions from people.
So, for those people who can’t seem to believe in physical things that they can’t see, it might be worth stopping to ponder just where all that schmutz came from. On that high-end air filter pictured above. Some of it is common household dust. Some of it is PM2.5, aerosolized air pollution around 2.5 microns in size. And some of it, for this filter, will be as small as the smallest aerosol particles that carry coronavirus.