I have an 1800 Center Chimney colonial house that has just had a pellet stove installed, the installer ran a 5" vent pipe off the back of the stove straight up the chimney and out the top, my problem now is that I no longer have the ability to close my flu or damper as it just hits the pipe so my Chimney is always open, I know I am losing alot of heat through this large gap. Is there anything I can do to safely close it off or pack around the pipe that wont catch fire but will effectively seal off that opening?