Drobe grow 5 square feet

High guys after scouting your forum an looking at all your delightful grow diaries, I am finding it really hard to find excuses to NOT grow my own pot, but before I even start buying equiptment I'd appreciate a little help with my setup.

Dimensions : 1.75 x 2.83 x 5.4 foot high giving me 5 feet squared of floor space

A 250w HPS 29000 lumens gives me 5800 lumens per square foot and...
A 400w HPS 50000 lumens gives me 10000 lumens PSF
now i've read that a plant can absorb about 7500 lumens and that the extra from 400w certainly wont hurt it at all.
My only concern is the heat that is given off by the 400w may be too much for my space, I obviously plan to have an intake fan at the bottom and an extractor fan at the top but have no clue as to the size i would need to keep the 400w's heat down. If someone could help me solve this I can get started on my home grow

Best way would be to have a vented hood with about a 150-250cfm pulling through it (depending on if you're getting a filter). To be honest there is no such thing as over kill when it comes to cabs. So I recommend a super sun 2 hood with a 6 inch centrifugal fan at about 400 cfm and 6 inch carbon filter. You can try and figure out a way to mount it inside or if ya wanna be a little less stealthy but still incognito then you can modify a box to hold the filter and fan inside of it and it sitting on top of the box.