it dosn't matter. i've seen them set up both as the exhaust intake and the exhaust end of the exhaust.

the best way to avoid smell leaks is to have a negative pressure in your grow room...

to do that you have your exhaust fan stronger than your intake. then any small holes were air exchange could occur will be intake vents. so no worries.

the filters work very well, and the slower the air goes through them the better.