The vented hot water storage system has a vent pipe that is open to atmosphere. The vent pipe is fitted to let the hot water expand when it is heated so as not to pressurise the system. SW1 Plumbers know water systems. In the majority of cases the vent pipe will discharge over the top of a cold water storage cistern usually through a return bend, but in some older fits it would discharge outside above the roof. Water coming from the cold water storage cistern feeds into the bottom of the storage cylinder through a cold feed pipe. This water re-fills any hot water taken from the cylinder. When cold water is heated from 0C-99C it expands by around 4% of the systems volume. In reality this means that at 99C the contents of a 200 litre cylinder would now be 208 litres. If this expansion was not relieved by using the vent pipe the storage vessel would pressurise and burst causing flood damage.


Unvented Hot Water Storage Cylinder.
The unvented hot water cylinders store water that comes straight from the mains water supply, heating it with electrical heating elements or using heat from a boiler. This produces high pressure hot water capable of supplying outlets with high flow rates of hot water. An SW1 Plumber is trained to work on both systems. The cylinders store water under quite high pressures, usually around 2-3 bar, and with this kind of pressure are able to supply water to outlets at high levels in a home, such as up in a loft, and at similar pressures to the mains cold water supply. These increased pressures also provide better quality showers, so there is no the need for a pump. Having both hot and cold water services fed from the mains, there is no more requirement for a cold water storage tank, and so keeps the loft spaces clear, and pipework down to a minimum.”