The air circulation was terrible in this unit from the factory. They only give you a hole about the size of a pencil in the upper rear. I drilled 3 holes 3/4 inch holes with a hole saw in the upper rear and on the side right around the area of my chip tray. The smaller holes where from the original mount for the factory vent. I drilled the same holes in a piece of galvanized and cut out a 5 inch circle. Now I can adjust intake and exhaust easily. I just spin the disc the open as much as I need. I got a perfect amount of smoke for the first time with my ribs since I can dial it in. The work quality should have been much better but I decided to do this about 20 minutes before the days dinner was to go in the unit.