A fin tube assembly has a core tube of elongated transverse cross-section having rounded leading and trailing sides, opposite flat faces, and opposite open ends for flow through the tube. A plurality of fins project in opposite directions from finned areas of the opposite flat faces. The finned areas terminate short of the rounded sides of the core tube. A first internal rib extends across the interior of the core tube adjacent one rounded side and a second internal rib extends across the interior of the core tube adjacent the opposite rounded side to separate the interior of the core tube into a larger central channel between the ribs and separate side channels between each rib and the adjacent rounded side of the core tube.