[steamer25]

Matthias Wandel recently did some experiments over several options. A decent furnace filter, when duct-taped to a box-fan, did surprisingly well:

https://www.youtube.com/watch?v=rDZ9yUdM2wA

It turned out that my local hardware store had a similar pre-manufactured offering with a slightly less Jerry-rigged aesthetic. We bought one for my son's allergies but I also noticed an improvement on the whole upper floor of our house. Box fans can move a lot of air. Furnace filters are cheap commodities with a large cross-sectional area that also allow a fair amount of flow.

[breput]

There seems to be two main use cases for a room-sized air purifier:

If you live in a polluted city or are affected by wildfires, having a box fan-sized model is almost a necessity. It is going to be noisy and unsightly but undeniably more effective. Having a few furnace filters laying around for air quality emergencies is probably not a bad idea.

For day to day use in a low pollution area, where dust or pollen is the major concern, I really like the little 120mm fan purifier. It runs 24/7, unobtrusively, and is really effective for what it does.

[vl]

Surprisingly, there are ultra-quite full-size fans as well. I bough Vornado fan from Amazon, and this is one of the best devices I ever had. On first two speeds it’s basically silent, I use it 24/7 to ventilate room with bad air flow in my house. It’s also Alexa integrated, but I never can remember the commands.