COAXIAL FLUES: AISI 316L BA stainless steel single-wall flues (thickness 0.5 mm). The “coaxial system” is made up of an internal smoke flue for venting flue gases and an external (support) flue which can be used to draw combustion air into the appliance or as a simple free coaxial ventilation section. The “coaxial system” must be assembled as indicated in the specific User Manual and based on the characteristics of use. It can be used to create lined systems (fumes/air) operating in positive pressure.