My setup is a mostly indoor 15 foot steel chimney straight up only 3 ft of it pokes up thru the roof (12ft class A and 3 ft of double wall pipe). I have a surface temp probe and a stack probe 18 inches up from the collar. How could I possibly get a more textbook installation for a stove...15ft straight pipe all inside! I doubt that I have an air leak...I have checked the seals real good. Some anecdotal evidence that I do not in an overdraft condition is that I have burned some pallet wood and can keep the stack temps under 800 degrees with the primary air fully closed and top damper open. If I opened the primary air full with pallet wood I'm sure it would get super hot. I did a warm the house up burn last week with 6 biobricks and the stack temps were lower than I was getting with pallet wood. Honestly I don't know very much about this...my conclusions could be wrong.