thanks that makes sense.
I'll keep working on this. right now it makes 1-90, through a filter, then another 90. I checked on the resistance on the filter and it is next to nothing, what the tech said, so if I put 2 filters in line I get double next to nothing.
so I need to find out how much SP I get with 2 - 90's. If it is not more than 0.500-in, then this fan should work.
I just hate trial and error. you know what they say "at first you don't succeed, try, try, try, try, try, try, try...................again"