Unvented hot water cylinders are now the most popular option for new hot water systems.

They operate at the same mains pressure as the incoming cold water supply (typically 3 bar or so) and therefore provide excellent water flow rates without requiring a header tank in the loft space or additional pumps. In 'direct' units the water is heated by one or more electric immersion heaters.

They come into their own when a gas/oil boiler is either not available or too expensive to install, or in situations where the requirement for annual GAS SAFETY CHECKS of appliances, flues and pipework is considered onerous, for example at rental properties.

Also suitable for a wide range of commercial applications such as hair dressing salons, canteens, washroom areas etc.

An English man named Thomas Hawksley invented a highly efficient method of heating for domestic hot water supply purposes in 1861.

Since then these systems have been utilised all over the industrialised world except in the U.K. due to legislation. It was not until the legislation of 1985 Building Regulations and the 1986 Model Water Byelaws were introduced, that permitted the installations of unvented hot water systems in the United Kingdom .

Now the installation of Unvented hot water systems in the U.K is commonplace with the systems providing key benefits to many system users.

Unvented systems are perfectly safe.

It is a highly efficient method of storing and supplying domestic hot water.

The installation and maintenance of the system should always be carried out by trained and qualified professionals to ensure that all legislations are met and your safety is put first.

In unvented hot water systems fed from the mains supply, the water flow rate and pressure at the tap is largely determined by the incoming mains supply.

As hot water expands during the heating process, the expansion of water is taken up by an expansion vessel or an air gap contained at the top of the cylinder.

The unvented system also incorporates a temperature relief valve (the equivalent of the open vent pipe on vented systems). This is designed to safely discharge water if it exceeds the pre-determined maximum temperature.