Heat-transfer characteristics during melting of magnesium chloride hexahydrate (MgCl2.6H2O = MCHH) have been determined for circular finned- and unfinned-tube systems. The effects of inlet temperature and flow rate of the heat transfer fluid (HTF) on the heat-transfer characteristics have been determined. Heat transfer from the tube to the phase-change material (PCM) is strongly influenced by natural convection of melted PCM, especially in the unfinned-tube system. The measured melting-front velocities in the unfinned-tube system agree well with analytical predictions. The amounts of heat storage in three different systems have been correlated in terms of Fourier, Stefan, and Reynolds numbers to provide basic data for designing unfinned-and finned-tube heat-storage units.