Stan, I encourage you to re-read Nelraq and Mayhem's posts above. I have a 28' class A six inch, 26' of it are completely enclosed in a heavy wall stone chase. My stove is a very easy breathing, pre-EPA, non cat stove with excellent air flow. I am often able to start fires when it is 55 degrees and falling, based on the barometric pressure trending up at the time. My routine starting point is 50 degrees or below. You are burning some wadded up paper near the flue exit before lighting your fire I assume?