Abstract: This patent covers a chimney in prefabricated modular elements, normally but not exclusively to be built outside buildings.The flue stack consists of two modular prefabricated elements (A,B) to be assembled by progressive raising. The first element (A) is consisting of an outer covering pipe (1) usually having a square cross section, an intermediate pipe (2) usually having a circular cross section and an internal liner (4) usually having a circular cross section, all pipes being rectilinear and interconnected by stirrups, while the hollow space between outer (1) and intermediate pipe (2) is filled with insulating material (3). The second element (B) has normally a shorter length than the first and consists of an outer envelope (pipe) (1), an intermediate pipe (2), both rectilinear, while the internal pipe (4) has a bend or branch at its lower end for connection to the exhaust of the various users.