How a water heater tank works

The principle of operation of a hot water heater is based on indirect heating¹ of the tap water that fills the tank, using hot technical water through a tubular heat exchanger located at the bottom of the tank.

The internal volume of the hot water heater is constantly filled with tap water and is under pressure. When the heat source is turned on, the hot heat carrier flows into the spiral heat exchanger, which cools down and heats the water filling the tank.

As the hot water heats up at the bottom of the tank, it rises and creates a circulation effect inside the hot water heater. The natural circulation effect ensures even heating of all the water in the tank, but the water at the desired temperature will only be reached after some time when the entire volume is heated.

If quick heating of even a small volume of water to the desired temperature is required, hot water heaters with a multi-layer heating device are used. In such tanks, the natural circulation effect is absent, and during heating, the boundary between the hot and cold water layer drops from the top of the tank to the bottom. This means that almost immediately after the heat source is turned on, hot water suitable for use will appear in the top of the tank.

With the start of water intake, the hot water heater does not empty, and the cold water from the water supply network enters the bottom of the tank, displacing hot water through the pipe in the upper part of the hot water storage tank. Due to the difference in densities, there is no intensive mixing between the accumulated hot and incoming cold water in the hot water heater.

Heating control is usually entrusted to an electronic regulator, which, upon receiving a signal from a temperature sensor built into the tank, turns off the heat source and circulation pump in its circuit. For more information on heating control schemes, see hot water heater connection diagrams.

A solar collector, heat pump, heat network, solid fuel, gas, or electric boiler can serve as a heat source for a hot water heater.

¹Indirect heating — heat transfer through a heat exchanger from technical water to tap water.