[jefftk]

> > A filter which captures 70% of particles with an air flow of 100cfm will capture the same amount of virus as a filter which captures 100% of particles with an air flow of 70cfm. Both will clean the room just as fast.

> It will not clean the room just as fast, it will take longer to clean the room.

Here are two different models:

A. Air moves sequentially. First you filter all of the air once, then you filter all of it another time etc. In this model, a filter with 100% efficacy will get everything in a single pass, and the CFM determines how long that pass takes, while a filter with lower efficacy will never get it all, but will get pretty close after a few passes. In this model you want high filtration.

B. Air moves randomly. At each minute, the purifier selects air from the room at random, filters it, and spits it back out. In this model, a filter with 100% efficacy at 70 CFM is exactly equivalent to a filter with 70% efficacy at 100 CFM, and you will often want to trade off efficacy for flow.

I think real rooms are generally much closer to (B) than (A), though of course somewhere in the middle?