Shouldn’t we be putting HEPA filters on every air conditioner and heater? Don’t HEPA filters take viruses out of the air?


Shouldn’t we be putting HEPA filters on every air conditioner and heater? Don’t HEPA filters take viruses out of the air?

In: Technology

The problem is not the virus lingering in the air, it’s people sneezing and people breathing in the aerosol, or people sneezing, the snot going onto surfaces and people touching the surface and then their mouths

They can only take out so much, and whatever happens to be airborne. The biggest concern are transfers from people to people or people to surfaces, not so much lingering airborne viruses.. Which is why we wear masks 😀

HEPA filters take damn near *everything* out of the air. [This]( is what a typical air filter out of a home AC unit looks like after I’m guessing around 3 months, which is the recommended time to replace them. That particular filter is pretty dirty so it might be closer to 6 months, it’s hard to tell exactly. When I worked in a small aquarium store we had to change all three filters *every* month and they looked worse than the one in that picture. After two months they would get so clogged that it caused the evaporator coils to freeze.

That’s a filter that only catches pet hair, clumps of dust, fuzzies, and *maybe* pollen if you spend $20 or $40 for the good ones designed to catch it. Pollen is [orders of magnitude larger]( than viruses. So not only is the HEPA filter catching the viruses, it’s catching every single thing larger than the virus that gets caught up in the filter. If all of that stuff *larger* than pollen will clog a filter up that quickly in a commercial setting, you can imagine how much faster they would clog when they have to catch all the particles down to the size of a virus.

That would be an outrageous cost, since HEPA filters are so much more expensive, and they would have to be replaced so much more often. We had three AC units for a *small* store. A large store will have both more units and larger units that require specialized (ie: more expensive) filters.

There isn’t enough benefit to justify that cost. Not all of the air gets circulated all the time, so viruses will still linger. It won’t remove viruses from surfaces. It won’t get rid of the viruses immediately after a sneeze. It really won’t accomplish much.

Not worth the trouble or expense. The problem is that HEPA filters only catch things sized 0.3 microns and up, but the corona virus is smaller than that – 0.125 microns. Still, the virus is usually coughed or sneezed out on larger particles which the filter might catch, except that those particles tend to fall to the ground pretty quickly anyway. And finally, even if the HEPA filter could catch all the particles, it wouldn’t clean the air quickly enough to prevent someone coughing from infecting someone else who’s nearby at the same time, and it wouldn’t help if you touched a contaminated surface and then rubbed your eye, etc.

This makes a couple assumptions, like every place having forced-air HVAC. A lot of factories don’t outside of offices. It also depends on that HVAC operating, which most will regularly cycle on and off, or maybe even just be turned off, weather permitting. It also makes the assumption that all air will go through the system and thus be filtered. It doesn’t because it doesn’t have to, HVAC systems will typically just naturally mix hot/cold air with the ambient air at the outlets and let it all just kinda diffuse itself out and about.

Also, HEPA filters are usually expensive, and you would need a hell of a lot of air systems of adequate capacity and thus HEPA filters of adequate capacity to get any appreciable effect in, say, the 30-40 million cubic feet of space in the plant I used to work at.

The cost:benefit ratio just isn’t there 99% of the time. Spending that money on some basic polypropylene masks and adequate supplies of hand soap and cleaning agents for shared tools/computers/controls, and pushing hard on hand washing and self-accountability would have a much better effect at minimizing everyone’s risk.

To that end on the handwashing, the food industry has been teaching employees the best possible practice for years. From length of time and warm water, to even saying to use the paper towels to turn the faucet off (dirty hands turn it on after all) and even to grab the door handle with.