Hot water tank

A hot water storage tank (also called a hot water tank, thermal storage tank, hot water thermal storage unit, heat storage tank and hot water cylinder) 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, 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 40 to 60 °C (104 to 140 °F), and are connected to the domestic cold water supply.

Where the local water supply has a high content of dissolved minerals such as limestone, heating the water causes the minerals to precipitate in the tank (scaling). A tank may develop leaks due to corrosion after only a few years, a problem exacerbated by dissolved oxygen in the water which accelerates corrosion of both tank and fittings.

Typically hot water storage tanks are wrapped in heat insulation to reduce energy consumption, speed up the heating process, and maintain the desired operating temperature. Thicker thermal insulation reduces standby heat loss. Water heaters are available with various insulation ratings but it is possible to add layers of extra insulation on the outside of a water heater to reduce heat loss. In extreme conditions, the heater itself might be wholly enclosed in a specially constructed insulated space.

The most commonly available type of water heater insulation is fiberglass, fixed in place with tape or straps or the outer jacket of the water heater. Insulation must not block air flow or combustion gas outflow, where a burner is used.

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