The Properties of Clay Flue Liners
The function of a chimney flue is to convey the products of combustion safely to the atmosphere. Chimneys lined with clay flue liners have done this and truly stood the test of time.
Over four million homes built since the 1940’s have chimneys with clay flue liners. Their durability is unquestionable. They are useable for chimneys serving heating appliances using solid fuel (including wood and peat), gas and oil with a working temperature of 600 °C. They can also withstand a soot fire of 1000 °C.
Acid resistance
The latest heating appliances are far more efficient than their predecessors and their exhaust gas temperature is much lower. This means that the flue gas temperature rarely exceeds the dew point - the point at which any vapour in the products of combustion condenses and turns to liquid.
This condensate is a surprisingly strong acidic solution present on the walls of the flue. Clay flue liners have a proven durability, with an inherent resistance to acid attack, giving noproblems with corrosion or disintegration of the liner body. When other flue liner materials are used which have far less resistance to acid attack, such as cement bonded aggregate, the durability and performance of the chimney may be seriously impaired.
Impermeability
Clay flue liners have an impermeable body which does not allow condensates or flue gases to pass through to cause acid attack to the outer fabric of the chimney, which can result in structural deterioration and ugly, permanent staining. They are tested for gas tightness at a differential pressure of 20 Pa and a maximum leakage rate of 0.002 m 3/sec. m 2, after being thermally tested (BS EN 1457 Type A1 N2).
Heat resistance
Soot and condensate deposits, particularly from solid fuels, on the inner wall of the flue liner sometimes re-ignite, causing a “chimney fire”. Clay flue liners have a natural resistance to excessive heat and provide an ideal barrier against the spread of a chimney fire into the building. Clay flue liners will withstand a thermal test that simulates sootfire conditions at a temperature of 1000 °C for 30 minutes.
