Most important thing is to have a flow of air going through. So youll want a fan blowing in fresh air at the bottom, and a fan sucking out hot air at the top opposite side. The cool tube will remove hot air, but radiant heat will still heat your plants. you really have to play around with fan powers until they can handle the heat ur cabinet creates. Intake holes must be big enough to supply ample air flow, so having more sucking out and creating suction isnt all that great, as there will be less air coming through the intake.