Their purpose is simple and known to all. They aim to eject from the building the combustion products generated by any machine and any source used to heat the environment. Simple and essential in their task, chimney flues have evolved in recent years to cope with the complexity of heat production systems and the consequent need for smoke evacuation. Precisely for this reason, even the chimney flues are now required to provide superior performance, as is the case with the double-walled stainless steel models featuring an intermediate layer of thermal insulation or air gap. The stainless steel models, which can also be installed outside buildings, are flanked by versions in ecoceramic and refractory ceramic materials that are ideal for any type of fuel. On the other hand, plastic flues are intended for condensing boilers and for kitchen outlets, in consideration of the low temperature of the outgoing fumes as well as the aggressive environments and corrosive condensation. The dimensions, available space and the diameter of the different models are important considerations when choosing a chimney flue.