How does an indirect hot water cylinder or tank work?

Calorifiers and cylinders are terms that are used interchangeably. They essentially refer to the same thing. Equally an indirect hot water cylinder is the same thing as an indirect hot water tank. A calorifier, indirect fired hot water cylinder or tank is a water storage unit with a coil that is heated by an external heat source. This external source – usually a boiler or renewable energy source – heats liquid (water or solar liquid) that passes through the coil. Water is heated as it passes over the coil.


Sometimes calorifiers, indirect fired water cylinders or tanks have two coils that are each linked to a different source – such as a boiler and a solar water heating system - to improve reliability and reduce overall heating costs.


Hot water storage tanks sometimes called buffers do not have a coil. They essentially only store water and will be linked to either a direct or an indirect fired hot water system to supplement hot water storage volumes to suit large demand applications. A well-insulated hot water storage tanks improve the overall security of your system as they can cope with a high demand for hot water.