I'm going to replace my 16.5"x20"x48" supply plenum. It looks like a spider as it has 10 pieces of flex duct attached to it 6 on one side and 4 on the other. I'm doing the work my self, I'm going to order from Airtite there airtight takeoffs with damper to start off right and I'm having a new plenum built. The problem with the existing plenum is it's condensating and it's moldy right at the plenum connection. My question is do I stagger the take offs one at the bottum one at the top or should they be all in a row down the middle?