VPD? I wish I would have thought of the middle door at first. I've been trying to figure out which side would be best for veg or bloom. The South is the outside wall so that would be cooler, for bloom. My exhaust fan Vents to the outside through the buildings sewer vent. That was a lot of work. Right now I'm trying to figure out air flow from north to south side. I'm guessing that veg side would need the fresher air from the floor level, more than flower side? Right, definitely vent from the top.