Grow room temp

I have a Closet that is about 3' X 3" about 6 feet tall, equipped with a 400W HPS bulb and ballast, two fans circulating air inside the room, the only problem is a lack of ventilation. Any ideas on how to keep the temp down in the room without leaving to door of the closet open at all times.

install ventilation

Ya gunna need something to get hot air out o that room,Have a look at a carbon filter! serves two purposes filters smell, extracts hot air from room.. bingo.Good luck

Ventilation, yes. Your room is 54 square feet so the ideal fan would move at least 162 CFM a minute but you could get away with less.

Mount your exhaust fan near the top and make some intake holes near the floor (cause hot air rises and will help with circulation). Make sure your intake hole(s) are larger than your exhaust so if you are using 6" exhaust fan - make sure your intake hole is larger than 6" and multiple passive intake holes are better than a single large one. So in our 6" exhaust fan example - three or four 3" intake holes would work great.

Two more bits of advice:
1) the less ductwork you use the better (saves on fan life and increases the fans effectiveness
2) get a glass reflector cover and use an exhaust fan to vent just the lights!

well make that three -
as lewtra mentioned you're going to have to deal with the smell. You can either install a carbon filter on the inside before the exhaust fan (so all the air gets sucked through the carbon filter before being vented outside). That is the more stealthy way. Or you can run duct work from the exhaust fan to the carbon filter on the outside -- depends on your situation and how much room you have in your box.

Mostly good advice, but IMHO you need a bigger cross section for a passive air-intake. Ideally the passive intake should be at least 3-4 times the area of the powered exhaust.

A 6" powered exhaust duct equals a bit over 28 sq. inches - so the passive intake should be at least 85-113 sq. inches, even 140 sq. inches is not really overkill. And remember - bigger inlets pass air more efficiently then multiple smaller ones, in theory anyway!

ive got the same problem lads i got a closet bout the same size as urs
with a 250 hps and a 125cfl
with one fan
nd let me tell you its bluddy hot in there
nd is it alright for the temp to stay around
85 even 90 sumtimes so any info tht comes on this page helps me and you

and i havnt really got money for extract fan but i no i do need one we both do
mines like a fukin fire hazzard
but it hasnt dun note to my babies

yet