Abstract: A finned heat exchanger for increased heat transfer from liquid to air, includes of a plurality of stacked thin plates of conductive metal sheeting which are provided with stamped and drawn, slightly conical collars of elliptical, oval or other oblong cross section. The plates are stacked and assembled with the collars of each sheet forcefully pushed into the collars of the adjoining plate, thus effecting tightly closed ducts for the passage of the liquid. The thus-created ducts are arranged in rows and columns, wherein the long axes of the oblong cross section are inclined towards the center line of each column at an angle of 12.degree.-16.degree. to the left and to the right in alternate columns, and wherein the ducts in the rows are staggered in the direction of air flow, every second duct being disposed in forward direction by about half the length of the long axis of its cross section.