It kinda depends on how you want to set up your system and alittle more information about what your using such as wattage of lamp would be helpful, but I'll take a shot at your question. With the availabilty of two fans I think I would go with a enviorment that will lend to the usage of Co2 if not now then perhaps in the furture. Ofcourse I don't know if you are running some sort of cooltube or aircooled hood because this will only work with one. I would use the larger fan for primary exhaust of just the lamp, that is I would run it like this ...
Fresh Air---->Hood--->Out of the grow area.
Then use the smaller fan to exhaust the grow area with a passive intake of roughly 10 inches for the 5in fan. So it would run...
Passive intake-->Inside tent-->Carbon filter-->outside of grow space. No duct between the passive intake and the carbon filter ofcourse.
Set them both on variable speed controllers and use either a thermostat or a thermostat combined with a timer to use with the smaller fan. This way you can intermiditely exhaust the grow space and introduce Co2 (either DIY or a more costly version with a monitor and controller).
Then........if you don't have an aircooled hood or cooltube. I would go with the larger fan on a variable speed controller and thermostat to exhaust the grow space and use a passive intake of 16 in or so. So that would go...
Fresh air---->passive intake--->Inside tent--->Carbon filter--->Outside. Better to pull than push through a filter in my opinion.
I'll go into detail about it if you want but there are lots of threads...search..Is it better to pull or push through a carbon filter
With alittle more info you'll get more responses. Hope this helps.
