attic ventilaton design with fan

[SkullMesaRanch]

I was under the impression that I could just use large triangular gable vents on my simple (with simple trusses) rectangular house and barn.  Going through the calculations I need 950 sq in of inlet and 950 sq in outlet ventilation for the house.   These vents don't provided anywhere near the passive ventilation required by code.  I don't like the idea of putting vents in the roof. 

 

Adding a fan should reduce the vent requirement considerably. 

I found a source that said 1 SF NFA(net free area)  for every 300 CFM.    So if my attic is 1985 sf/150=13 SF.   How does the sent size come into play when you have a large fan in the attic?

 

 

Edited April 28, 2023 by SkullMesaRanch
add more info

[Richard_Morrison]

It really doesn't, because it's based on intake area, not exhaust CFM. If you need 13 SF, then you may need to provide larger gable vents, vents at exterior rafter blocking, ridge vents, soffit vents, dormer vents, etc. There are number of options and you need to decide which works best with the structure and architectural style you are dealing with.