On my son's humungous oil tank hog smoker, he has three chimneys, and a big firebox on each end of the 275 gallon oil tank. He put a pivoting flat piece of steel ontop of each stack (like old tractors & dozers used to have). He controls how much heat he wants coming from the left or right firebox by adjusting the pivoting plates on top of each stack & by cracking either the left or right firebox door. I never thought having to crack one or two doors open was a bad thing. It works good like that.
BC
BC