In most cases the relining process is completed because the system was damaged by a chimney fire. Most chimneys have a terra cotta liner system and in the extreme temperature ranges of a chimney fire the terra cotta breaks. The broken liner then will need to be repaired in order to safely use the system. The process includes all or some of the following......
LINER SELECTION- The liner selection is based on two variables.
What kind of system vents into the system?
What is the venting area required for the system?
What vents into the systemis required because not all stainless steel liners are created equal. Stainless steel comes in several types and alloys which need to be selected for individual systems. The two common types are 304 grade and 316 grade.
304 can be used to vent ONLY wood. It is a heavier wall liner and can be used for most wood applications.
The NFPA requires several things for a safe liner installation.
All liner manufactures require that the liner be insulated with either fireproof insulation or thermix poured insulation. Each have there own advantages and disadvantages. The only requirement manufactures state is a liner does not have to be insulated if the previous liner is intact and NOT damaged and can be left in place to provide insulation to the chimney itself.
The installation process simply involves determining the type of stainless steel needed and the venting area required as well.
In some circumstances the old liner needs to be removed in order for the new liner to pass down into the chimney cavity. There is a special tool that allows this done safely with out disturbing the rest of the chimney system. Once the old liners are removed the new liner is prepared with insulation and armor and either taken to the roof and lowered down or can be pulled up from the bottom with a winch system. The bottom is sealed off and the top is sealed from the weather and a rain cover is installed.
The Chimney Clinic
the 316 liner can be used to vent oil, wood or gas where the 304 can be used only for wood. There is a cost difference in the liners where some companies will use a lesser expensive liner for a installation neglecting the fuel type. A gas furnace can turn a 304 liner into swiss cheese in a matter of a couple years.
What is the venting area of the system is required because every appliance whether it is a fireplace or a wood burner requires the proper venting area to maintain the proper draft. An appliance with a outlet must retain the same outlet size. So for example if a wood burning stove has a 8" outlet the liner must then be 8" NFPA fire code states that the liner may not be reduced in size and cannot be larger unless the venting area requires it. A fireplace uses a mathematical formula to figure out its area. The height and width of the fireplace opening then dictates the venting area needed. In most cases a fireplace liner will be between 10"-12".
Relining your chimney is a standard practice in which you replace the exciting flue liner which is either wore out, nonexistent or damaged with a new flue system. The new liner in most cases is stainless steel. However there are several replacement lining systems on the market as a alternative to stainless. The most common of those are a poured liner which uses a mixture of mortar and insulation and a form. The most common however is relining with stainless steel which is more commonly used and much more efficient.