A calorifier is a heat exchanger which heats water indirectly by circulating is over a heating coil or multiple coils. The source of heat can be water or steam, heated by an external heat source, contained within a pipe immersed in the water. the two bodies of water or steam do not mix. (touch each other)

In hospitals and factories where steam is already being generated for other uses is can also be used to heat the water by the indirect method.

The calorifier may be a continuous coil of pipe or a cylinder within a cylinder with an annular space between the two vessels.

 

With the vertical hot water cylinder, the steam enters the coil though the top connection. the strainer or grit trap removes any solid matter suspended in the steam. The steam then passes through the inlet valve which is thermostatically controlled. the thermostat prevents overheating or boiling of the stored water.

A steam trap, fitted near the outlet of the coil, prevents the steam from leaving the coil until is condenses.

In a hot water cylinder which contains a steam coil, the coil must be able to be removed for descaling. this is more likely to occur using steam because the coil is working at a higher temperature than with the conventional hot water system.