A hot water storage tank is a water tank used for storing hot water for space heating or domestic use.
Water is a convenient heat storage medium because it has a high specific heat capacity. This means, compared to other substances, it can store more heat per unit of weight. Water is non-toxic and low cost.
An efficiently insulated tank can retain stored heat for days, reducing fuel costs. Hot water tanks may have a built-in gas or oil burner system, and electric immersion heaters. Some types use an external heat exchanger such as a central heating system, or heated water from another energy source. The most typical, in the domestic context, is a fossil-fuel burner, electric immersion elements, or a district heating scheme.
Water heaters for washing, bathing, or laundry have thermostat controls to regulate the temperature, in the range of 104 – 140 °F, and are connected to the domestic cold water supply.