We have a new Shelter wood burning furnace only been in use a about a year and a half now. The issue we are been having is what I call burping. The stove puffs smoke out from the door, intake at the bottom and from the pipe. Not all at once and it is not consistent. We have trouble shot this issue many times. Extended the chimney, change the pipe and made sure the angles/length are all to code, dry wood and clean the chimney and pipes every frequently. We have even taken apart the pipe and checked the draft up the chimney and have a good draft up? We are at a loss and don't know what more to do. Can you give us any help?