The DPC stainless steel series is a concentric flue system fit for fumes exhaust and for comburent air inlet of type C and condensing heat generators, and gas fireplaces: the combustion products get out through the inner duct while the air necessary to the generator combustion gets in through the gap between the inner duct and the outer one. The gap between the inner duct and the outer one can also be used as a free section of ventilation in case of lining of existing chimneys or technical spaces with positive pressure operation. The available diameters are Фi=80 and 100 mm and the series is complete with all the special elements and the accessories required by both applicable rules and ordinary plant requirements.