I had a 120mm cpu fan exausting from vent in top and passive intake on lower vent. But since venting is not a problem at all for these lights its more air circulation that i worry about. So I put the 120mm fan in the lower intake and I have passive out take. This gives more airflow around and under the canopy, it also makes the tent balloon out a bit which reflects more light back to the middle of the tent rather than away to the sides. It also allows breathing room between the hanging cfls and the side of the tent so I dont worry about fire risk etc. I know its unorthodox but it seems to be working real well. The out take vent is also 2" smaller than the intake, creating positive pressure in the tent.re: Quitekeen - are you running any intake or exhaust fans or just passive intake?