What is an unvented cylinder?
An unvented hot water cylinder is a pressurised system that is fed directly from the cold water mains. This means that hot water can be delivered at mains pressure giving greater performance for your shower and bath, especially if you have more than one bathroom.
Unvented cylinders do not require a cold water storage tank which saves you space and also offers more flexibility when installing the cylinder. As it does not rely on gravity, it can be pretty much installed anywhere in the house. Using the mains pressure also gives a better flow rate and therefore greater performance for your shower. The water is heated either by an immersion heater or mains central heating, although other forms such as solar thermal technology or heat pumps can also be used.
Unvented cylinders do require an expansion vessel to be fitted to allow for the expansion of water in the system as it heats up. They also have other safety aspects such as pressure relief valves and twin thermostats therefore it is also important, like any other appliance, that they are serviced annually to ensure they are functioning correctly.