Afraid I'm still not getting what I need. Here's some more info. I am moving into a 2 bedroom townhouse. 1 bedroom will be used for it's intended purpose, the other will be turned into a study. The room that is being turned into a study, I will be using that walk-in closet for my grow. I would not per se need to keep the door (to the closet) closed, but would like to have the option if guests show up. So my thoughts were that I could leave the closet door open, and maybe put one of the el cheapo intake/exhaust fans in my window in the study to get some fresh air in there, but would this be enough?

Even if I build a cab, where am I exhausting the air to? Remember, no holes in the walls. Also, the room (the study) will be air conditioned.