HVAC any techs on here? what is acceptable air flow drop? 1-5% I think is the max. I have a air purifier that accepts donut/ring types of filters, the original hepa looks/sized like a semi truck kind of thing. I can plug fan-filter combo into a kill-a watt meter and check and see differing draws with variously dirty filters, which alter with filter loading. A years old hepa which is more filter than a typical car one is only few watts more draw since new. I notice little diff new/old auto unless visibly dirty. They do get a gassy smell, and perhaps this affects their performace as well. How long life? 1-3 years, seals will deterioate and even if media good seal may be not.