Water Heater Expansion Tank

expansion tank
A tank used in a closed-loop solar heating system that provides space for the expansion of the heat transfer fluid in the pressurized collector loop.
An expansion tank or expansion vessel is a small tank used in closed water heating systems and domestic hot water systems to absorb excess water pressure, which can be caused by thermal expansion as water is heated, or by water hammer.
A tank designed to absorb excess pressure due to thermal expansion (e.g. closed system).

water heater
An appliance for supplying hot water for purposes other than space heating or pool heating.
a heater and storage tank to supply heated water
Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have many uses.