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Unvented Hot Water Systems

In an unvented system, a vessel is filled with cold water directly from the incoming water main. The vessel is kept under pressure from the incoming water supply and heated either by immersion heaters (a direct model) or by a heat source located outside the vessel (an indirect model). Examples of the latter might be a gas boiler, solar energy, and Aga etc.

The 'vessel' to which we refer normally takes the shape of a cylinder. In an unvented mains pressure system the cylinder must also be regarded as a pressure vessel. This type of cylinder is referred to as 'an unvented cylinder' because it is not vented to atmosphere in the same manner as a normal copper cylinder be. Unvented means exactly that.

The unvented cylinder will have pipe work connected to it that will carry the heated contents around the property to various taps and outlets. As soon as an outlet is opened the pressure of the incoming cold water to the cylinder forces(displaces) the contents of the cylinder (hot water) out and towards the open outlet.
Unvented hot water cylinders have to withstand considerable internal forces. For this reason most are made from stainless steel (as opposed to copper for a vented/gravity cylinder) utilising the tensile properties of the metal. This is why you should never try pressuring a cylinder unless designed for this purpose. To do so would introduce a very real risk of explosion all unvented cylinders must be fitted with pressure relief equipment & must be fitted by a Bpec qualified installer. To ensure that unvented cylinders are fitted correctly, safely and by competent installers the Government introduced Building Regulations (G3). These Regs cover any vessel that contains more than 15 litres of hot water under pressure. Adept is a Bpec qualified installer of unvented systems & meets with all necessary regulations, details of which can be provided at any time.