I have a question regarding my new Osburn 2400 insert. When reloading or repositioning logs when the stove is not up to temp. I open the door about and inch and no smoke enters the room. But then when I open the door all the way a lot of smoke comes in. When the stove is up to temp. this does not happen, no smoke enters the room and it is easy to reload, obviously the stove is operating more efficiently at this point and not creating as much smoke. My question is, is this normal? And what can I do to eliminate the problem? The stove is vented through a 6 inch flex liner inside an exisitng exterior masonry chimney. It is not insulated. Suggestions...