You cannot really see it but on top of the metal vertical box is the first vent with an adjustable plate over the stack as you suggested but it hampered the venting of the firebox to much. The vertical box was off a gas smoker that I no longer use. I am going to put back the brick section with a better door and use the vertical section in another smoker. The vertical brick section was one of many vertical brick units that I have tested. I attempted to add on a horizontal section and I am working out some of the bugs. I have tried several different venting arrangements of the horizontal section including a vent above the grill, mid way to the grill and below the grill. The venting of the grill area both vertical and horizontal seems to be to directly affect the flavor of the barbecue.
What are thoughts on that?
Randy