A heat exchanger apparatus includes an inlet header, an inlet connection connected to the inlet header, an outlet header, an outlet connection connected to the outlet header and a plurality of serpentine tube bodies. The plurality of serpentine tube bodies interconnect and are in communication with the inlet header and outlet header. Each serpentine tube body has a plurality of straight tube sections and a plurality of U-shaped return bend sections. Each one of the straight tube sections and each one of the return bend sections have an elliptically-shaped cross-sectional configuration. The plurality of serpentine tube bodies are arranged in a juxtaposed manner with consecutive ones of the serpentine tube bodies contacting each other at a point defining a series of stacked common planes disposed parallel with one another.