Too much intake or not enough?

Setup:
small cab (24"dx24"wx40"H) with 4 x 4in passive intakes.
170 CFM inline fan pulls air through a 3" cool tube and pushed down into the carbon filter.

I had the door open and I put a blanket over the door. after an hour I came back into the room, and the blanket was completely sealed over the door pushed in from the fan. is this a sign I need more passive intakes? I'm thinking my passive intakes are not moving enough air, but I heard that negative pressure is good. Anyone have experience with this?

with a passive intake, you want the vent to be twice the size of your exhaust vent.

that sounds about right! i can do the same thing if i hold a t shirt up at the door it will be semi sucked into the door way. also i like to smoke outside the room and watch the smoke being sucked into the grow room. haha

That's good if it has that kind of a vacuum going on. If you don't have that your odor control will be near impossible.