[sl1ck731]

I would assume the majority of people (in the US, anyway) are already filtering their air enough through their central air to make any additional "room-sized" filtering negligible.

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.

[dr_orpheus]

Dense HVAC filters make your HVAC systems run much less efficiently. There is less airflow and less heat transfer (either cooling or heating). Anyone that has come to service my air conditioner or furnace has always checked the filter and recommended never getting a denser filter. The filters in the HVAC system are more there to prevent your furnace from getting clogged up with larger particles than to help the indoor air quality.

[showerst]

In a previous house I rented, we swapped the furnace filter for a much finer one (from 8 to 13 on whatever scale they market these things in), and it made the HVAC system run noticeably worse. Lower airflow, noisier, etc. It seemed to me that the intake system couldn't keep up with the reduced flow of the denser filter.

Could moving to a coarser filter but adding room filters be useful in that context?

[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.

[cptskippy]

That assumes that your HVAC runs regularly. Apart from deep summer and winter we rarely run our house HVAC.

We have a filter that runs constantly at low speed because we have pets and without the filter there would be issues for members of my family.

[0xffff2]

Do a large majority of people in the US even have central air? It's virtually unheard of to have an HVAC system in older buildings in California.