to Da Horse:
I thought I would talk a bit more about carbon filters. We know what a carbon filter is doing, right?
Super dried, "activated charcoal" will attach organic vapors from the air flow, to the carbon particles. If you have access to an oven to hold it, you can bake them out, and re-use.
Do carbon particles care which way the air is flowing? They do not.
So, when someone says you can use them in positive or negative pressure, push or pull mode well... you CAN. But, the trick is to know why we do stuff and not depend on sales opinions and patter.
Say I was running a room at positive pressure, for what ever reason I am using the filter. (can't think of one) Then the positive pressure is what PUSHES the airflow over the carbon. But, positive pressure as nice as that might be for some good reasons(???), is not good for a cannabis grow for some very good reasons.
Mainly we are trying to control smell. So, Positive pressure would be against us.
We use negative pressure, and pull exhaust on the space.
Also, reducing pressure, lowers temps but positive pressure will increase the temperature in the space. So while the maroons at the hydro store are good at repeating what the sales rep said, I bet they would be very hard pressed to answer in what situation you would find a PUSHed carbon filter in indoor agriculture.