PURPOSE: To increase heat transfer performance with a low cost, by a method wherein fins are provided vertically or oblique-downwardly while a wire material is wound around the outer surface of the tube with an arbitrary lead angle in accordance with necessity.

CONSTITUTION: A tube 1 is used horizontally or in a slanted condition. Fins 2 are provided radially in the upper half of the tube 1 as shown by a diagram while the fins 3 are provided in the upper 2/3 of the lower half of the tube 1 so as to be slanted downward in the same manner substantially as shown in the diagram so that liquid, condensed on the upper and lower surfaces of the fins, drops quickly. The inclinations of the fins are made as large as possible. A metallic wire material 7 is wound around the outer periphery of the tube 1 solidly in accordance with necessity while the wire material 7 is welded to the tube 1 through spot welding at some places. The wire material 7 is used both for the reinforcement of the tube 1 and the disturbing of the flow of cooling water to increase the heat transfer area of the tube and improve a heat transfer efficiency. According to this method, drain water may be discharged quickly to the bottom of the tube while the heat transfer efficiency and the heat transfer area of the tube 1 may be increased.