[lotsofpulp]

>Similarly they make some very dense HVAC filters if standard ones aren't catching the level of particles you need, so I'm not sure what the purpose of these filter-fan things are for most people.

These are a scam, especially all those 3M filtrete ones. Air handlers in homes and most other HVAC applications are not made to also serve as tiny particulate filters, so it will make the whole HVAC system slow or even stop since it won't be able to get the air flow it needs to function.

[djannzjkzxn]

I believe you that the HVAC isn’t designed for such a filter. But a few months back my home was in the path of smoke from some wildfires. The AQI went from 200 to 0 after I installed a filter and ran the house fan for an hour. Also, the furnace doesn’t have to work very hard here because of the mild climate, so I never have much of a heat bill anyway. It would be a bummer if the furnace died because of it running out of spec, but I’m skeptical that the risk-adjusted cost of that is higher than the cost of standalone filtration units.

[lotsofpulp]

This page has a decent explanation of the problem:

https://www.pvhvac.com/blog/whats-the-best-air-filter-for-yo...

All the commercial HVAC technicians I speak to say to use the cheapest non fancy filters if your goal is to maximize life of the HVAC system, but I'm sure it all depends on everyone's specific system and how the return is and whatnot.