picture of running tap

Hot Water Cylinders

Indirect Hot Water Supply
The indirect system is probably the most common form of dhw, allowing a boiler to be used also for central heating purposes. The storage vessel is the heart of these systems and consists of a special cylinder in which is fitted a heat exchanger. The heat exchanger allows water from the boiler circulating in the primary pipework to pass through, but not mix with, the water in the cylinder itself. Thus, in effect, it really consists of two systems which appear to join at the hot storage vessel.

Water is heated in the boiler and conveyed to the hot storage vessel via primary flow and return pipes by gravity circulation (convection currents) or by the use of a circulating pump. The water supplying this primary circuit can be taken from the cistern, which is located in the roof space.

Direct Hot Water Supply
A system which uses an immersion heater installed into the hot storage vessel. This behaves in a similar way to the element in an electric kettle, when the desired temperature is achieved, sensed by a thermostat, the element is switched off. It is essential that the heater element reached low down near the bottom of the storage vessel because it will only heat the above the depth to which the element will reach.

Unvented Domestic Hot Water Supply
With the unvented system the water is taken directly from the mains water supply. There is no open vent pipe or storage cistern where the expansion of heated water can be taken up. Therefore some form of expansion vessel needs to be incorporated. The advantages of these systems are the higher pressures obtainable at the draw-off points, the use of less pipework and the fact that less time is required for installation.

Indirect Hot Water Supply


Direct Hot Water Supply


Direct Hot Water Supply