A hot water storage tank

The method comprises the steps of: providing one or more water usage draw cycles corresponding to historical water usage with respect to time and each having a temperature and volume requirement; using the historical cycles to predict future draw cycles; determining an energy requirement for each predicted future draw cycle; and providing at least one reference energy price forecast over a future period of time. The method further comprises the steps of determining a temperature profile of the hot water storage tank required for each of the predicted future draw cycles; determining for each predicted cycle a total energy purchase cost based on the at least one reference energy price forecast; and selecting a heating schedule to meet the temperature and volume requirements of the predicted future draw cycles with the minimum total energy purchase price. The method is particularly for use with stratified hot water storage tanks of a domestic hot water system. An alternative method of selecting a heating schedule with the minimum total energy purchase cost is also claimed.