A diffuser is provided for use in a thermal storage tank. The diffuser includes a fluid inlet to receive a flow of liquid into the diffuser, and a fluid outlet to discharge the flow of liquid out of the diffuser into an internal volume of the thermal storage tank. A flow circuit extends between the fluid inlet and the fluid outlet. A plurality of flow sections are sequentially arranged along the flow circuit. Each one of the plurality of flow sections defines a cross-sectional flow area for the flow of liquid. The cross-sectional flow area within any one of the plurality of flow sections is greater than the cross-sectional flow area within any of the plurality of flow sections arranged upstream of said one of the plurality of flow sections.

A diffuser is provided for use in a thermal storage tank. The diffuser includes a fluid inlet to receive a flow of liquid into the diffuser, and a fluid outlet to discharge the flow of liquid out of the diffuser into an internal volume of the thermal storage tank. A flow circuit extends between the fluid inlet and the fluid outlet. A plurality of flow sections are sequentially arranged along the flow circuit. Each one of the plurality of flow sections defines a cross-sectional flow area for the flow of liquid. The cross-sectional flow area within any one of the plurality of flow sections is greater than the cross-sectional flow area within any of the plurality of flow sections arranged upstream of said one of the plurality of flow sections.

The present invention provides an electric boiler having a heating element surrounded by a thermally conductive inner container to define an inner passage about the heating element, the inner container having an inlet and an outlet for a flow of water and is arranged such as to cause water received at the inner container inlet to flow along the inner passage in close proximity to a surface of the heating element, the boiler further comprising an outer container in which the inner container is substantially located, the outer container defining an outer passage about at least part of the inner container, the outer container having an outlet into the inner container wherein the outer container is arranged such as to cause water to flow along the outer passage in close proximity to a surface of the inner container, such that water received in the boiler makes at least a double pass through the boiler to increase the potential heat transfer to the water.