ADB Heating & Plumbing | Vented & unvented hot water cyclinders
A vented hot water storage system incorporates a vent pipe which is open to atmosphere. This vent pipe is used to allow the hot water to expand when heated without pressurising the system. In most cases the vent pipe discharges over the top of a cold water storage cistern normally by means of a return bend, however in some older installations it’s discharged externally above the roof. Water from the cold water storage cistern is fed into the bottom of the storage cylinder by means of a cold feed pipe. This water replenishes any hot water drawn from the cylinder.
Unvented hot water cylinders store water supplied directly from the mains water supply, and heat it using either electrical heating elements or with heat from a boiler. This provides high pressure hot water supplies capable of feeding outlets with high flow rates of hot water. The cylinders store water under relatively high pressures, typically in the region of 2 to 3 bar (20 to 30 metres head), and as such can supply water to outlets at high level, such as in a loft space, and at similar pressures to the mains cold water supply. The increased pressures also make for better quality showers, without the need for pumps. With both hot and cold water services fed from the mains, there is no more need for a cold water storage tank, keeping loft spaces clear, and pipework to a minimum.