Hot water storage tank and a diffuser

A hot water storage tank defining a primary storage volume, at least one heat source positioned in and operable to directly heat water in an upper portion of the primary storage volume, a hot water outlet positioned in the upper portion, and a pump operable to draw water, from a lower portion of the tank into a heat transfer device, situated in said upper portion, in which the heat transfer device does not enclose the heat source or a further heat source and is configured to enable the transfer of heat from heated water in the upper portion to the drawn water;

• a feed pipe fluidly connected between the heat transfer device and the lower portion of the hot water storage tank to enable water to be pumped from the lower portion to the heat transfer device, the feed pipe being positioned inside and extending into the lower portion of the tank in which the heat transfer device includes a diffuser including a mixer portion for causing mixing of drawn water with heated water in the upper portion to enable the transfer of heat from heated water in the upper portion to the drawn water.