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Photo at left shows a blown out section of tile. Photo at right shows a flue liner destroyed by a severe chimney fire. Tiles with breaks can no longer contain the products of combustion and the chimney must be relined before further use.
Vitreous clay tile liners are not made to withstand SUDDEN changes in temperature at or over approximately 500 degrees. Tiles will crack and break during a chimney fire, and sometimes sections of tiles and mortar joints will blow out. There may be "hairline" cracks in the flue, which, when heated during normal use will open up to large cracks.
Stainless steel liners and chimneys are not impervious to the high temperatures a chimney fire can produce. Although most are tested to 2100 degrees, a flue fire can reach temperatures much higher than that - perhaps as high as 3,000 degrees. If stainless steel is subjected to temperatures above 2100 degrees, damage to the liner may occur. The actual composition of the stainless steel will change, and warping in the liner or buckling of seams may occur. You may also notice a discoloration in the steel, which, according to metallurgist Bill Paynton, could mean a change in the molecular structure of the steel. If a stainless steel liner has been subjected to a flue fire and has been damaged, it no longer meets U.L. listing requirements and replacement will be necessary.
The liner keeps heat and smoke inside the flue, where it can vent to the outside. If the liner is no longer a sealed system, it may allow smoke to escape through the cracks in the tile to the area inside the "chimney chase". This area cannot be cleaned during chimney cleaning, so any creosote in this area formed by smoke will not be removed. You can see the potential for a more dangerous chimney fire the next time. Smoke and carbon monoxide can also escape into the living space of the home.
Make sure to have your chimney cleaned at least annually, and do not use a tile liner with any type of wood stove or wood burning insert to avoid flue fires.