One 12" fan inside would work fine.

From the sound of your idea with the pipe through garage and to the door you will be needing to do some calculations on your own. There is some math behind exhaust work that is very important. It deals with length of run and how many bends in your ducting. It all relates to the CFM fan you need, especially since it sounds like there may be a good amount of bends there.

http://boards.cannabis.com/growroom-...g-hot-air.html
All to do about fans/exhaust.

Also remember that PVC when heated outgasses very toxic chemicals and will harm your plant. Make sure theres no PVC inside your tent.
GetThisOrDie Reviewed by GetThisOrDie on . Growlab 120 Ideas Okay so I plan on making my first indoor grow room, I am looking for a few answers here to some random questions and also some helpful advice. so here's the tent - GrowLab GL120 here's the hydroponic system I was going to use 5 of them in the tent to start with - WaterFarm Complete here's the lighting I was thinking - Magnum XXXL 6" 400w Switchable Complete System Okay so I am growing this in my room, me and my wife dont want something too loud, what can I do about that? from what I Rating: 5