think 4 x 8 x 2 = 64

therefore u need to expel 64 cubic feet of air an hour (i think)

However, something that small isnt going to help extract all that heat ur hps is going to make.

IMO, u want one that expells about 500 cubed feet an hour
chonged Reviewed by chonged on . 1st Post, Venting question First, I would like to give a HUGE thanx to everyone on the boards here. Being completely ignorant in the art of indoor horticulture, I came here looking for answers and tips. After combing the posts, many of my concerns have been laid to rest. Now, for my NOOB question: My growing area is 4'w x 8'H x 2'd, though I plan on capping the height at 6' to maximize light concentration. I dropped the cash (now broke) for a 400w HPS light, which will be used throughout the growing process (post Rating: 5