Unvented Hot Water System January 03, 2018 Until the mid-1980s, the majority of UK water heating installations involved cistern-fed open vented low-pressure systems. While a large number of these systems remain in use, the fact that they are gravity fed means that they are often ill equipped to cater for modern lifestyles, leaving the end user frustrated as a result. More recently, combination boilers have become a `go to'; fitted on the assumption that they will provide instant hot water. However, for properties with two or more bathrooms, it's an assumption that can be misplaced, with demand from two or more outlets at the same time potentially outstripping the system's capabilities. Constant supply Thankfully, there is a solution — in the form of an unvented hot water system. Designed to provide a consistent supply of powerful, mains pressure, high-flow hot water, they offer a viable alternative to lacklustre or miss-specified systems. End users get the satisfaction of being able to draw equally balanced mains pressure water from every outlet, and the everyday luxury of invigorating high-performance showers and fast filling baths. In traditional open vented systems, mains water is delivered direct to the cistern and then on to outlets at a low pressure, which is determined by gravity. Flow rates are reliant on the static head — the fixed vertical distance between the water level in the cistern and the appliance outlet. As a rule of thumb, 10 metres equates to roughly one bar of pressure, meaning that a shower one metre below the cistern will deliver just 0.1 bar of pressure.Stored under high pressure However, in unvented systems, mains water is delivered direct to a cylinder and stored there under high-pressure until it's required. When weighing up the pros and cons, remember that unvented systems do not require a cistern tank and therefore are not susceptible to issues such as float valve jams, blockages in the pipework and cistern water freezing. They also eliminate frozen pipes and are modern and hygienic, guarding against the threat of winter flooding and removing the potential hazard of contaminated cisterns. There is also plenty of flexibility in where to site a cylinder garages, airing cupboards and lofts are all popular locations. Safety measures The term 'unvented' actually refers to a water heating system that doesn't include an open vent pipe. As a result, cylinders are designed with a series of safety control devices which, among other things, prevent stored water exceeding 100°C. Large unvented cylinders can only be installed or serviced by engineers with Building Regulations Approved Document G (G3) training. Qualified engineers receive a numbered, photographic identification card, which is valid for five years, making it a worthwhile investment. It is a criminal offence to contravene Building Regulations. This includes the notification of the installation and commissioning of a new unvented system, or plans to alter existing systems. This notification can be made by the installer, or by a Competent Persons Scheme if the installer belongs to one. It is important to note that Water Regulations require any approved contractor to provide a certificate of competence, and any electrical wiring or testing should be carried out in accordance with the relevant British Standard. Other relevant standards are BS EN60335-2-21 for electrically heated storage water heaters, and BS EN60335-2-73 for immersion heaters.