Just for the record I have an interior chimney and this fall I removed the unit, insulated the liner and put in a block off plate over the damper. There is a lot more heat and longer burn as well as a cleaner chimney. Do it right the 1st time and you will be happy. The place that did the install basically lied to me as well as the hampton rep himself. After doing it right I am more estatic with the performance!