Fan Help

I am going to have a 3x3x5h grow box with a 400watt hps light. I am going to use two fans one for intake and one for exhaust and i know that computer fans are good to use. however i have no clue what computer fan to use, how much power i need. Anyone who can point me in the right direction would be a great help.

3x3x5=45 cubic feet so i think most 12-18v pc fans come in around 125cfm which is perfect for a small room although you may wanna get or make a cool tube