Abstract: An S-shaped heat exchange tube with improved heat exchange efficiency. The tube is provided with a quartet of entry dimples in a first segment of the tube adjacent an inlet end of the tube, a first series of dimple pairs in a second segment of the tube and a second series of dimple pairs in a third segment of the tube.The quartet of entry dimples lie in a plane approximately perpendicular to a longitudinal axis of the first segment. At least the first three dimple pairs of the first series are graduated in depth, with the first dimple pair in the first series being provided adjacent to the first segment and having a depth less than a depth of the second dimple pair in the first series. The third dimple pair in the first series and all dimple pairs following the third dimple pair in the first series have depths which are equal. Depths of all dimple pairs in the second series are equal to the depth of the final dimple pair of the first series.

Abstract: A forced air, wall heater includes a heat exchanger which has a plurality of tubes. Each of the tubes include substantially parallel aligned runs and at least one return section between adjacent runs. The return section is aligned generally perpendicular with each of the plurality of runs. The heater also includes a blower positioned for blowing air directly toward the return section to maximize the mass flow rate of air over the return section. At least two of the runs are offset both laterally and in the direction of air flow with respect to each other. The ordering of tubes differs in at least two positions within the exchanger.