I live in Indianapolis, IN, and I have been getting new roof estimates. I have quotes that say I need 13 exhaust box vents (50 in nfa), and quotes that say I need 41 of the same box vents. Why such a big difference. My attic has 3525 sq ft. I have seen the formula for minimum nfa as either 1:300 or 1:150 ( IRC Code). Which do I use. Can’t find local building code. Can anyone help? Thanks, Brad.