Chimneys are an integral part of the building, even more so as the discharge of flue gases from the heating system to the outside is of high safety relevance. Therefore high standards are set, which modern chimney systems achieve and therefore combine safety and warmth. The following characteristics are important for a chimney system:
- Acid resistance: Pollutants in the flue gas either develop during the combustion process or are already included in the combustible. Together with moisture they might develop aggressive acids that condensate on the chimney wall, attacking the material. Acid resistant materials do not react to those acid attacks.
- Moisture resistance: If the flue gas falls below a certain temperature (thaw-point), which is the case e.g. with condensing boilers, die containend moisture condensates on the chimney wall. Moisture resistant materials keep the condensate inside the system and thus prevent the penetration of wet into the surrounding materials.
- Soot-fire resistance: Using solid fuels like wood, soot particles might deposit on the wall of the chimney. If the chimney is not cleaned regularly or not completely, these particles might spark off, causing an unwanted soot-fire incident. Soot-fire resistante materials endure the high temperatures of a soot-fire (more than 1000°C) and just let a small fraction of the heat out to the environment.
- Durability: The above mentioned incidents test the material over a long time. Suitable materials for chimneys are resistant to those conditions and thus achieve a long lifetime and high durability. Some manufacturers even guarantee the functionality of certain materials for 30 years!
Over time, certain materials have proven to be suitable for chimneys. Modern chimney-systems started with the usage of clay and ceramic materials, today also metal and plastic have earned their place. The latter is mainly used for condensing boiler technologies, while ceramic and metal are suitable for all applications.