Chimney liners are required to safely remove combustion byproduct outside of your home. Byproduct can come from the use of a fireplace or other appliances such as a water heater or a furnace. There are two common types of chimney liners: clay flue, or metal.
Clay flues are what you will find in most chimneys especially for the use of a traditional fireplace. They come in a variety of sizes, with the most common being 8” x 8”, 12” x 12”, and 8” x 12”.
The flue starts above the firebox, and is stacked in 2 foot sections as the chimney is built. The top section will protrude out the chimney cap, and will often have a metal rain cap attached to prevent water or varmints from entering.
The top liner will occasionally need to be replaced due to the weather exposure, while the lower sections will often last many decades before needing to be replaced.
Metal liners are used for home appliances as well as highly efficient wood burning stoves or fireplaces. For lower temperature applications, such as a water heater, aluminum is commonly used. For a wood burning stove of fireplace, a higher strength stainless steel is required due to high temperatures. Stainless steel liners have a variety of benefits compared to clay flues such as efficiency, durability, and low maintenance.
When a clay flue liner needs to be replaced completely, the most common approach is to install a metal liner. To install a new clay flue liner, the whole chimney would need to be rebuilt, which is not cost effective. A metal liner can be installed down into the original to take its place. If the size of the metal liner required is to large to fit, or the original is falling apart, it may be necessary to break up the original flues and start from scratch.