Abstract: A cooling device for use in tubular hot gas conduits which are made up of a plurality of longitudinally arranged side by side abutting pipes includes a plurality of registers arranged in spaced relationship along the length of the pipe and extending into the pipe from one side thereof into closely spaced arrangement in respect to the opposite side. The registers each include a plurality of U-shaped pipes which are interconnected and arranged in the direction of flow and which are connected externally of the hot gas conduit through respective inlet and outlet headers.