More 2cent opinion. What diameter and length is your exhaust flue? Did you try running without the OAK? I don't use one because the damper is barely open, so I'm not really taking much air out of the house. Have you tried disconnecting the OAK atttached to the air inlet and running it that way for a while? Maybe your not getting enough air because of the OAK and that's why you have to open the damper. My thoughts, as to why your stove would operate differently than the others of same model, "Air" incoming or outgoing is not operating the same as other Yorks.