Abstract: A heat exchanger element for exchanging heat between a fluid circulating in the element and a phase-change medium in a reservoir housing the element is formed of a plurality of spiral coils of flexible tubing disposed horizontally, one above the other, in a vertical stack. One end of each spiral coil is in communication with an inlet manifold and the opposite end is in communication with an outlet manifold. Preferably, the manifolds are disposed vertically, extending the height of the stack and side-by-side. Preferably, the manifolds are adjacent the outer periphery of the vertical stack of spiral coils. The spiral coils of the stack are wound alternatively clockwise and counterclockwise from a first radially outermost turn to a last radially innermost turn and arranged in pairs, one above the other. One spiral coil of each pair has the first radially outermost turn connected directly to the inlet manifold and the last radially innermost turn connected directly to the outlet manifold.