Vented Indirect

The traditional 'vented' hot water cylinder operates with a header tank and generates lower water pressure than an unvented cylinder. In 'indirect' units the heat source is an external boiler that circulates hot water through a coil heat exchanger within the cylinder. In practice indirect units also have an electric immersion heater as a back-up in case of boiler failure. Indirect cylinders are generally more expensive to purchase and install but usually result in faster reheat times as much more heating power is normally available from a boiler than from electric immersion heaters.