I have the same dimensions as you with the same size fan only I am running 2 400watters with euro reflectors. The temps are stable at 77 on the inside the room with the temp outside the room steady at 70.I have a 2.5 inch s-pipe made out of PVC on the bottom to serve as my intake. I tried using a 4 inch line with a 4inch fan but it made my temps increase just a tad so I took it back off. I also have a 6 inch booster fan on this set up as well just because after I added the carbon filter the temps started rising up to 83:thumbsup: