Flue tiles are known to crack for several reasons, most often, is a sudden occurrence. A sudden occurrence is classified as a chimney fire or lightning strike. Flue tiles are made to expand and contract, but when heated up to rapidly, as occurs with a chimney fire or lightning strike, they expand too quickly and crack. Once this occurs the integrity of the chimney liner is compromised. It allows for the smoke and heat to get into the internal workings of the chimney structure. Over time this can lead to the wood around the chimney structure to dry and reach combustion stage. If the issue is not addressed in time, it can lead to spontaneous combustion, and a structural fire. When chimney sweeps, home inspectors, and fire fighters, find cracked tiles, their 1st and most often recommended fix is a stainless steel reline.
Why stainless steel liners? Stainless steel liners, when properly installed, draft better, and are more efficient than flue tiles. They also insure that in the event of a future chimney fire, a homeowner is not looking at having to replace the tiles again. Stainless steel liners also come with a lifetime limited warranty. The warranty is void if the liner is not cleaned and inspected annually by a chimney technician.
The proper installation of a stainless steel liner starts with the proper sizing of a stainless steel liner. This requires an accurate measurement of your fireplace opening. We then follow the International Residential Code (IRC) book for the proper sizing of a stainless steel liner. The IRC states that for a chimney to draft properly that the flue system must be in a 12:1 ratio for a round flue. Many times the original flue that is in the chimney was not properly sized, this can make for a challenge in getting the properly sized liner installed. We then remove all the clay flue tiles from the chimney, this is to ensure for the proper installation of the liner, and ensure that the existing flue tiles do not collapse at a later date and ruin the liner. There are a lot of companies that do not properly size the liner and fail to remove the flue tiles form the chimney. If a company does not remove the old flue tiles it can lead to big issues down the road.
The most important part of installing a stainless steel liner is choosing the proper insulation for the liner. There are two choices available. The first is a cerwool blanket. This is similar to the insulation used on the space shuttles. The second choice is a vermiculite and mortar based insulation called Chim Mix. Both insulations do not allow for the transfer of heat. We most often use a cerwool blanket, but in some cases where we find chimneys that were not constructed properly or have wood in them we use Chim Mix. The insulation of a stainless steel liner is required by the manufacturer as part of the warranty. It is what gives it it’s UL listing. There are companies that do not insulate the stainless steel liner. By not properly insulating the liner it allows for the heat to radiate into the chimney cavity, which over time can lead to the drying out of the wood around the chimney structure and lead to spontaneous combustion and a structural fire.
For cosmetic reasons we always put a flue tile at the top of the chimney. It looks funny and is an eye sore to see a pipe sticking out the top of a chimney. We also insulate around the top of the liner inside the tile. A stainless steel rain cover or top mounted damper is installed as is required by the manufacturer.