Abstract: Bent-out wall in the region of a substantially rectangular burner opening (2), wherein the bent-out wall (1) is formed by tube walls (3) and the tube walls (3) consist of tube-fin-tube combinations welded in a gastight manner and the tubes (5) thereof are flowed through by a cooling medium, wherein at least part of the bent-out wall (1) along the two longitudinal sides (7) of the rectangular burner opening (2) is formed by means of prefabricated tube wall segments (4) and wherein the prefabricated tube wall segments (4) are machine-welded in the planar state at the workshop and are subsequently bent at the workshop to a wall bending radius (R) of 70-140 mm and a wall bending angle (W) of 110°-150°.