Abstract: A heat exchanger unit has tubes each having a body section and at least one of an inner pipe section and an outer pipe section extending from the body section and defining an opening at an end. Each of the inner pipe section and the outer pipe section has a first portion and a second portion adjacent to the first portion. The tubes are stacked such that the body sections are spaced from each other. Further, the inner pipe section is received in the outer pipe section such that the first portion of the inner pipe section overlaps the first portion of the outer pipe section, and the second portions of the inner and outer pipe sections are located on opposite sides of the overlapped first portions. The first and second portions of the inner pipe section have an outer diameter smaller than an inner diameter of the first and second portions of the outer pipe section.