3x3x6 grow setup questions ++rep

Okay so I am pretty new to this forum but I have been looking at other peoples posts for a few years. I finally decided to register and see if someone could help me with my questions.

My question is, I have a 3x3x6 wooden box I am growing in. I want to know what cfm duct fan I should buy and do I need to pull the air from outside the box to cool the lamp or can I just pull the air from inside the box through the cool tube? I will also have 2 small fans running inside the box. My light is a 400watt MH. Thanks for any help ++rep

I would go with a 500 cfm fan and it's best to pull from out side ur box that way ur not getting the smell from inside ur box and exhausting it where ever ur exhausting it

Thanks for your reply! And that makes sense, do you think that would be enough to keep the box cool or will I need another fan to cycle the air inside the box?

You should have some air exchange for inside ur box also need to replenish that co2

Okay thanks. I live in a place where growing is legal with proper parperwork etc. so i do not have to worry about smell much, Would I be able to use only one fan and have it pull through the cool tube? There is a 2x2 square cut out in the bottom of the box, so would that pull enough co2 in? Im just trying to avoid having to buy 2fans, I'm on a bit of a budget.
Thanks for the help!

Ya that will allow proper air flow for a budget I to live in a state with mmj but it's always best to cover the smell just my opinion

Okay, I hooked my 500cfm fan and its pulling If out through the cool tube.... My box is still at 84.7 inside. What he hell can I do to lower the temp....this wojld be my first grow and its.starting to seem like its more trouble than its worth.... Any ideas on how to fix this before I throw I The towel?