What is Chimney Relining? Do all chimneys need liners?
Chimney Relining is putting a new liner in the chimney. As ctsweep noted, clay liners are often found in old masonry chimneys and often need relined. Indeed, once a liner is cracked, it will probably need relined. Cast liners are another kind of liner that cracks. Another common reason liners need replaced is that they are not the proper size for the chimney/flue needs.
Do all chimneys need liners? It is highly recommeded. Liners reduce chance of chimney fire, improve effiency, improves flow off noxious gasses out of home, and reduce liklihood of needing chimney repairs.
For more info, see http://www.highschimney.com/chimneyliners.php and http://www.highschimney.com/articles/category/chimney-linings/
Traditionally, masonry chimneys had clay tiles that covered the inside of the chimney. These tiles were designed to seal the chimney structure and direct all the sparks, heat, gases and particles up and out of the home. The problem is that over time, the tiles crack or break due to weathering, heat and freeze cycles, and other factors. Once the break-down begins, your chimney can become dangerous to use and can require a new lining. Some older chimneys did not even have the tile liners, so they are a real hazard that needs immediate attention. Chimneys built before 1940 have a high likelihood that they were built without a clay liner. Every chimney needs a liner of some kind that is designed to fit the needs of the fireplace, stove or furnace that is venting through it.
