Air Filters For People Who Have To Work In Enclosed Spaces Right Now

[liquidcitrus]

So today I was idly poking around the Internet seeing how people were coping with the California wildfire smoke, when I saw this article on Wired by Adam Rogers, about how a "janky" box-fan-and-air-filter setup could filter virus-carrying sneeze/cough particles out of the air. For, say, teachers who are required to keep the doors and windows closed for "security" reasons during a certain present pandemic, this could be lifesaving. (HEPA filtration units would work better, but they are exceptionally expensive; these aren't as good but they're notably cheaper.)

I'm going to put an asterisk on this, though: picking a random air filter and taping it to a fan isn't going to work very well. Because the air filter is reducing the amount of air going in (as it needs to do, to do its job), the motor in the fan will work harder, causing it to overheat and eventually burn out. It's like trying to breathe through a drinking straw.

To be clear: if a 2 inch furnace filter is all you can do, it's still a lot better than nothing. So here's the short version, for the simplest kind of box fan filter:

Get a filter of "MERV 13" rating, which means that it at least tries to grab particles of the right size. (MERV 11 or 12 might do in a pinch, but don't filter as well. MERV 14+ are expensive and harder to find because they're only really used in laboratories and hospitals.) It should be about the same size as the fan, and as thick as you can afford. Make sure to use some weatherstripping - the foam tape usually sold for putting around door cracks - to minimize the amount of air that gets around the filter. Put it on the side that the fan sucks air in from, rather than the side that blows air out. Then tie or tape it in place.

Pictured: a box fan with a furnace filter held on by rubber bands and weatherstripping foam tape

But we can do better: let's get some more filter surface, so the fan doesn't choke. Here's another article, from the person who the reporter was interviewing, saying to use a filter that is as deep as possible - 4 or more inches, if you can, rather than 2 or 1. That'll help, because it'll provide more surface area. But what if you can't find a 4-inch filter?

One answer, from the CEO of a company that sells air filters, is this: tape together a bunch of smaller air filters!

Pictured: a box fan with a "cube" made of furnace filters sticking out the back

Someone who runs an air filter company would have a good reason to want to sell more air filters. And furnace filters in these specific dimensions might be hard to find. So maybe this isn't the best idea.

Enter an even jankier version: Tom Builds Stuff's duct-tape-and-cardboard-box version of the box fan filter!

Pictured: a box fan with two air filters on the back, all held together with cardboard and duct tape

You only need two filters for this one, and you don't have to get the exact same dimensions of air filters either. You should still do your best to get some that are MERV 13, and as thick as you can get, but as long as one of the sides is 18-20 inches, this will work fine. (This tutorial says to get 20x25, but anything from 18x18 to 20x36 would at least sorta work.) Put the 18" or 20" side vertical, and then follow all the rest of the instructions.

Hopefully this helps those of you who are being subjected to, I don't know, wildfire smoke or ridiculous management policies?