Abstract: A heat exchanger having a plurality of parallel pipes arranged in lines and strips of fin plates fixed to the pipes perpendicularly to the lengths thereof. Turbulence-forming structures are cut out of the fin plates and are bent up at 90.degree. with respect to the planes of the plates, such structures functioning as fin plate spacers and as baffles to direct a fluid medium of inferior heat transfer coefficient which flows in a direction parallel to the planes of the finned plates and perpendicularly to the pipes. The pipes are adapted to conduct a fluid medium of superior heat transfer coefficient. The turbulence-forming structures are disposed in lines on each side of the lines of pipes and in rows which are substantially tangential to the opposite sides of the pipes. The heat exchanger may have a plurality of lines of pipes spaced equally transversely from each other and transvetsely of the direction of flow of the fluid medium of inferior heat transfer coefficient.