Just to add to this...i hear that a rule of thumb is 100 cfm/sq ft of opening. So, with my 7' x 6' frontage, does that mean i need a 4200cfm fan
? Sounds like i would be sucked up against a filter. I am thinking more that it is per sq foot of filter opening...so if i had 4 filters with a total filter opening of 8 sq ft, then 800 cfm would suffice. Anyone?