In another scenario, if the first filter has an efficacy of just 15% and allowed a flow of 1200 cubic feet per minute, it would give us 180 cubic feet of clean air, as opposed to the 199 from the second one. 20/

The big difference is the bigger flow allowed by the first guy more than makes up for its lower effective filtration. That is why we want to check CADRs and not just effective filtration. 19/

So, every minute, the first guy delivers 1000 cubic feet air, 70% likely to be clean. So that is about 700 cubic feet clean air every minute. The second guy delivers 199.8 cubic feet clean air every minute. 18/

Hypothetical time. Say, there is a filter which picks out stuff you don't want with 70% probability. Another, filters the stuff out with 99.9% probability. Every minute, the first lets 1000 cubic meters of air pass through, the second lets 200 cubic meters of air pass through 17/

The CADR tells you the overall impact, taking into account how good the filter's efficiency is in the size range of concern and the flow rate through the filter. 16/

That sounds complicated. Which is why we talk about something called clean air delivery rate. Depending on the size of the pollutant of concern, a CADR can be calculated, following some standards (ahamverifide.org/ahams-air-fi...) 15/

So, based on the pollutant size of concern, we decide on a filter type. There will be a range of filters in this group. They may have different flow restrictions. The compromise we need to strike is the bet value of efficiency times flow rate. 14/

Let me take it to an extreme. You could have an impermeable plastic film - that will give you 100% efficiency but 0 flow rate. We certainly do not want that. 13/

We need to strike a balance of an optimal flow rate and filtration efficiency. 12/

There is air in the room, there are pollutant sources, the air cleaner is continuously passing the air through a filter, getting stuff out of air and doing it again while the sources continue put stuff into the air. 11/