According to Jon Cockburn, head of marketing for Heatrae Sadia, when selecting and installing water heating provision for a customer, point-of-use unvented systems will usually offer the best solution, particularly in situations where long pipe runs need to be avoided.
With many of today's homes featuring multiple bathrooms, householders require a powerful supply of hot water, without significant loss of performance if more than one tap or shower is used simultaneously. Furthermore, the trend for luxury bathroom products such as multi-jet showers and jetted air baths has also created a demand for systems which can produce large quantities of hot water and fast flow rates to operate correctly.

In addition to meeting the needs of the domestic householder, unvented hot water storage is also a requirement with commercial applications. In situations where there is high demand for hot water at peak times during the day, such as in a hotel, leisure centre, office, school or hospital, a large unvented cylinder - or several operating in sequence - can provide an excellent solution.

Unvented cylinder systems have proved to be extremely successful and this has resulted in a wide range of products being available on the market, but it is important to remember that they aren't all the same and don't all provide the same level of performance. Therefore it is important to consider a number of factors when choosing the right equipment.

Quality is always the key and because unvented cylinders store water under pressure, they need to be strong and robust in construction. Other considerations are cylinder material; the hot water performance; standing heat losses/insulation; flow rates; the length as well as terms and conditions of the guarantee and the quality of the manufacturer's after sales support and service.

All unvented water heating systems require an expansion volume to accommodate the water which expands when it is heated. In a traditional vented system, the expansion occurs in the cold feed pipe, resulting in a small water level rise in the cold feed cistern. However, with an unvented system, the cold water comes from the mains, so an alternative solution needs to be sought.

As water is non-compressible, the system needs to allow space for expansion, otherwise the pressure will rapidly rise. Under UK regulations this is not permitted and with unvented cylinders, it is necessary to allow for this expansion within the design of the water heating system.

In the majority of unvented systems, the expansion is accommodated with an expansion volume either provided internally within the water heating cylinder (commonly termed an air gap or bubble top system) or through an external expansion vessel.

Megaflo HE

Having been installed in more than 900,000 homes in the UK, Heatrae Sadia's Megaflo HE features an internal air gap system with floating baffle that ensures water expansion is accommodated, while at the same time minimising installation time. With a lifetime guarantee on the Megaflo HE's stainless steel cylinder* including labour, Heatrae Sadia believes to be the only manufacturer in the UK to offer this type of guarantee on an unvented cylinder.

In addition, Santon's PremierPlus with external expansion vessel has been designed for UK water conditions. Providing high resistance to corrosion, it gives cost effective mains pressure water heating for both domestic and commercial applications. Pre plumbed versions are also available.

Unvented cylinders also work with solar thermal water heating systems and both Megaflo HE and PremierPlus are available as solar versions for domestic and commercial customers seeking a 'greener' solution. Even if the customer is not ready to commit to installing a complete solar system, selecting solar-ready equipment so they can easily upgrade is a good recommendation.

* Excludes damage caused by scale