Abstract: A highly efficient heat exchanger susceptible of a variety of uses is provided by a construction including first and second spaced, parallel headers 10, 12, 114 and 140 and a plurality of substantially identical serpentine conduits 18, 104 having at least three generally parallel runs 24, 105 and terminating in opposed ends 20, 22, 106, 108; 130, 132. The conduits 18, 104 are in generally spaced, side-by-side relation. One end 104 of each conduit 18, 104 extends to and is in fluid communication with the first header 10, 114, 140 and the other end of each conduit 18, 104 extends to and is in fluid communication with the second header 12. A plurality of serpentine fin sheets 30, 120 are located so as to extend between an associated pair of the conduits 18 in thermally conducive relation therewith.