I think zem is giving you some good advice, and its making me start to think. My last setup was a 150w mini cab and it had a passive intake that was 4-5 times the size of the exhaust fan, an 80 cfm inline fan, and I had absolutely no smell leaking. I should add that I did have a grill with a pre filter over the intake somewhat restricting airflow. I think I should ditch my intake fan and just make the hole bigger like zem says. I'm always lookin for ways to cutdown energy consumption. I must be able to get the same amount of airflow, I just have to make the intake the right size. I think I'll just gradually make the hole bigger until I reach the same temps I got with the intake fan.
If you get a chance zem could you elaborate on the last bit of your post? Did you mean that the 80 cfm fan was so much smaller than the 240, creating too much negative pressure essentially starving the plants? I mean I really only want enough to prevent odor leaks right?. Could you also give an educated guess as to how big a passive intake you would need for Simp's room dimensions using a 250cfm exhaust and maybe just a thin prefilter over the intake to keep out dust/bugs. If not I'll just use the old trial and error method i spose. Thanks.