Phase change materials (PCMs) have the ability to absorb and release a large amount of thermal energy over the phase transition. This might be an innovative solution to shift the power demand to off peak period and reduce the stress on the electrical grid. Limited research work has been carried out to investigate the impact of PCMs and/or enhanced PCM on the thermal performance of hot water tank. Numerical simulations have been carried out to thoroughly investigate the impact of a number of design and operational parameters on the thermal performance of hot water tank. Although PCMs offer the potential of having higher thermal inertia, the low thermal conductivity squanders that potential. The addition of either pure or enhanced PCMs shifts the power demand to the off-peak periods. This is mainly due to the high thermal inertia of PCMs which keeps the water temperature from plummeting. The simulation results demonstrate that the integration of enhanced PCMs to the hot water tank could shift the power demand to the off-peak for a longer period of time compared to pure PCMs due to the higher thermal conductivity and the enhanced heat transfer rate. (C) 2014 Elsevier Ltd. All rights reserved.