Think of it this way. You have a fan to move air. One end draws, the other blows. Now we have a way to move air and also know the direction it is moving. Ok, what air do we want to move? Hmmmm...... out of the grow area, yep. Now the air we want to move out of the grow area probaly smells, yep, smells. On top of the smell we have heat created by the growlight. But.... the lamp is in a coolable hood! How lucky are we?!? Ok, we have stinky hot air, a carbon filter, air coolable hood and a way to move air. Now how should we hook this all up, hmmm....... Like Lahoja said........