Vented and Unvented Cylinders

Vented and Unvented Hot Water Systems

David Black from Thermsaver takes a look at the rise of vented and unvented domestic hot water systems. UK domestic hot water provision has come a long way from solid fuel back boiler circulation to a vented cylinder in an airing cupboard. With the rise in new build properties and availability of gas from the North sea in the 1960’s, saw great developments in the gas fired boiler heating industry, including open vented domestic hot water cylinder systems. With the increase of en-suite facilities and bathroom improvements have made showering a part of the lifestyle of most homeowners. Most installs within the current UK housing stock are based on vented systems, but the high pressure showering requirements have seen the introduction of unvented system installs. When an unvented hot water system is installed, the hot and cold water supplies take the water to the taps and showers at the same mains water pressure. As cold water from the mains is delivered to the domestic hot water cylinder, the water is heated and when the tap or shower is opened the water is delivered at close to mains pressure. This pressure is not dependent on the head of the water, which equates to the height of the storage tank above the outlet in the roof space. As the water is heated it expands, this is where an internal or external expansion vessel comes into it, with a temperature and pressure safety valve fitted into the cylinder.

Vented or Unvented?

Unvented hot water cylinders can be indirectly heated by a boiler using oil, gas or LPG, but due to safety necessities solid fuel appliances are not an option. Unvented cylinders must conform to the safety rules as stated in the Building Regulations. These specify the need for a pressure reducing valve, a non-return valve, temperature and pressure relief valve, an expansion relief valve, a fundish and an expansion vessel. A secondary safety measure is a shut off valve between the main heat sources and the cylinder in case water temperature goes beyond set limits. There is an increasing trend for the installation of ‘renewable ready’ cylinders, installed for normal use but has the connections for future renewable use. As a result even more competence is required off the installers where renewable's are used for domestic hot water heating. The installer must be able to use the correct installation method in order to meet Building Regulations G3. There are undisputed advantages to fitting an unvented cylinder system such as level pressure at hot and cold outlets. Improved flow rates of hot water due to higher pressure, quicker filling baths, and improved storage in roof, quiet running and quicker installation. Water availability and the pressure at which it is delivered to the home is dependent on the utility supplier.

Vented Cylinders with added value

Installing an vented or unvented hot water cylinder completed with alternative storage hot water system offers added value for both the installer and the homeowner. To view the full range of vented and unvented cylinders available to purchase please visit the Thermsaver website. You can also contact us directly on 01698 300 100 where one of our team will be more than happy to help you with your questions.