Air intake question

[pot2010]

I've read numerous threads about this but can find a definitive answer. I plan on having an active exhaust with a carbon filter at about 200 cfm, my grow box would be about 72 in high x 40 in long x 30 in wide and use about 10 cfl's. I keep reading that a passive intake will work just fine but I would rather use a computer fan with a light trap to get air in. To get negative pressure would I have to use a lower cfm fan? Will negative pressure still occur if I have 1 or 2 fans circulating the air inside?

Everywhere I read people say to use passive intake but in a lot of grow boxes I see people use fans? Is using a fan for intake fine?

 

[SnowBender]

the 200 cfm will handle the cab with no need for intake fan(s), unless the intake has a long duct run. if you want to use intake fans you can, its just not necessary.
intake fan on a cab is nice if the room the cab is in is hot, that way when your working in the cab cool air is still coming in from the ductwork. (assuming intake is from a cooler space than cab of course)
internal fans will not impact your exhaust cfm's

 

[pot2010]

So I can use an intake but it's really not needed? It's just a little confusing for me because I see a lot of websites that offer grow boxes with intake fans and a lot of the dyi boxes here people made use them even if there isn't a long duct for the air to travel.