I had a wood stove installed and vented through my exhisting fireplace. A new metal pipe was installed all the way up and the installer insulated it between the pipe and the flue. He neglected to install a block at the bottom where he removed the damper. I asked him to install a block and he suggested it was so tight up in there, that it would be better if I just stuffed it with unbacked fiberglass insulation. That did'nt sound right to me so I checked the insulation and it stated "not for use in airspace between metal chimney and the flue. The reason I want to block it is, there is a strong odor from the chimney, because the top is insulated between the metal pipe and the flue at the top. There is no way for the odor to escape. Any suggestions as to what material I can safely use to "stuff" the damper area behind my stove? It will have to touch the pipe the same as a sheet metal block would.