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Posted By wg_bent,
Jan 13, 2006 at 7:00 PM
Resource for this? not faced, just raw fibreglass.
Unfaced fiberglass Melts at around 1100 degrees and I don't know what temp it can catch fire.
Chimney Fire is 2000+ degrees, so decent chance fiberglass may melt during a chimney fire if in contact with liner.
Mineral Wool insulation (same technique as fiberglass but different material) melts at over 2100 degrees and will maintain integrity during a chimney fire.
Lastly, neither stops air flow. If one wants something to stop air flow, use a piece of sheet metal.
A chimney fire can reach over 2000 degrees inside the liner, the outside during one will be cooler just don't know what the outside would be.