Flue Liners in Your Masonry Chimney
A chimney flue lining is a clay, ceramic, or metal conduit that is located on the inside of your chimney. Its job is to contain the combustible gases that occur in afire and direct them outside. A liner also protects the walls of your chimney from heat and/or corrosion. The installation of flue liners in chimneys has been recommended since the early part of this century. But recommendations are not always followed and some chimneys can still be found that are unlined.
Terra Cotta Flue Liners
A common material used to line a chimney in new construction are terra-cotta clay flue tiles. Other materials can also be used including: ceramic, metal, or cast concrete.
Flue Liner Damage Caused by Thermal Shock
Clay tiles are not good at rapidly absorbing or evenly distributing heat while temperatures rise in your chimney. A rapid temperature rise causes clay to also rise in temperature at a higher pace on the inside rather than on the outside of the tile. As the inside is heating up it begins to expand. Uneven heating can produce unequal expansion and may make the flue tiles crack or split.
This is called thermal shock.
Using a chimney with a liner that has been damaged or is compromised in any way can result in:
- A masonry chimney that expands and contracts, as it heats & cools can result in pieces of a cracked flue liner to fall out! The unlined areas of your chimney become hazardous and can create chimney fires or can block the flue and cause gases to back up into your living space. Carbon monoxide could leak in your home.
- Flue gases that leak during the use of of your heating system. A cracked flue liner, allows gases to pass through the chimney walls. Gases can be acidic and will eventually corrode the masonry.
- Heat from the cracks can transfer to the chimney walls. Flue liners act as insulation between the hot flue gases and your chimney walls, but when these walls are overheated, a fire can start.
A Word of Advice
Never use a chimney that doesn’t have a flue liner or has a damaged to the lining! Your chimney system is an important part of your home heating system and should be checked annually by a CSIA Certified Chimney Sweep and cleaned as needed.