How big of fan should I get?

I've got a 2x2x2 veg box that is air and light tight. I'm running 225-450w CFL's w/ lots of ducting. I wanna use a 4" vortex but don't know what the proper cfm would be. I DON'T want it to overheat.

I'm thinking this might work?
http://www.ebay.com/itm/4-6-8-10-COMMERCIAL-GRADE-Inline-Fan-Speed-Control-Hydroponics-Blower-Inch-/290927453266?_trksid=p2054897.l4275

Any 4" ought to work. but not if it is truly air tight. You need passive intake, some place for air to get in.

Intake should be in the bottom 10% of the grow area while exhaust should be top 10%. The exhaust can be expelled from anywhere but it should draw from the top. Say if you have ducting hanging in the top but can put a hole there. Just hang open end in the top and run the ducting down to where you have a hole. Place the fan where the exhaust hole is.

I'm just using an inline can(6")fan to exhaust my 4x4x6.5ft tent. I leave mine on 24/7 and the circulation fan in the tent comes on with light timer.

i would go for a 5 or 6 inch it might be a little more than you need better safe than sorry
i had a 125w in a bigger cupboard than you have for a mother plant

when closed it was getting over 85f
it takes time for the heat to build up but it will get hot without good circulation in a closed box even with just 125w

peace