BOILERS & HOT WATER Building breakdown:

Key considerations when specifying hot water solutions

Every building is different with any number of combinations possible when it comes to water composition, fuel and water supply, and that’s before you consider the usage and demand for hot water from end-users. As such, a one-size-fits- all approach cannot be taken, and specifiers must consider several factors before committing to a particular hot water solution. It’s also crucial to not overlook the legal requirements which need to be met in the manufacture, installation and operation of unvented systems. Let’s take a look at each variable in more detail:


When it comes to heang and hot water provision in the light commercial sector, no two buildings are idencal. With this in mind, Roy Marsden, product manager at Heatrae Sadia, explains the consideraons that need to be made when it comes to specifying the best unvented water heater for the building in queson

Considering fuel

What we often discover is that specifiers have preconceptions around fuel types. However, all fuel types can be utilised when specifying or installing an unvented storage system, whether it is oil, LPG, gas, electric, or a renewable source of energy.

Water supply

One of the most important considerations in the specification process is water supply. As such, specifiers must ensure it is of adequate pressure and provides a suitable flow rate to meet any periods of peak demand. With an unvented system, both the hot and cold supplies are taken from the main supply, so the supply should be adequate to meet both the hot and cold peak demand simultaneously. It’s also important to consider the application and how this impacts usage and demand. For example, while hotels may have extremely high hot water usage over a period of a few hours during the morning and evening, a school has set opening and closing hours so its pattern of hot water usage is likely to be fairly regular and continuous without noticeable peaks in demand. However, it is important to establish whether catering is involved as this would have an impact on peak demand.

Sizing and recovery

Sizing and recovery essentially go hand-in-hand. In order to assess the size of the vessel required to meet the end user’s hot water needs, you must assess the maximum demand, the frequency of delivery, and the recovery time required. While recovery requirements will usually dictate the heating power required, this can also be dependent on the fuel type used and the output available, especially where electricity is the primary heat source, and the maximum power available can be limited.

Water treatment and water composition

The local water composition will determine what unvented hot water system is specified as well as any subsequent treatment that is required. For example, filtration, water softening (ion exchange) and water conditioning (either chemical, electronic or magnetic) may need to be taken into account.

Key things to look out for in terms of water composition include the chloride level (high levels can attack stainless steel), the water hardness (this will dictate the amount of scale deposition), and the level of suspended particles (filtration may be required to remove these). Thankfully, most pressure reducing valves will include a strainer mesh to prevent particles impairing the operation of the valve.

Control of bacteria growth

While a tank may be well-designed and compliant, if it’s installed in a poorly designed system, bacterial growth can

become an issue. However, control of the conditions for bacteriological growth is achievable, whether it’s through changing thermal conditions or via chemical methods of disinfection, or UV treatment in large commercial installations. From a thermal perspective, water should be stored above

60˚C to prevent bacterial growth within the storage tank. However, it should be considered that water above 52˚C can scald so a means of controlling the hot outlet temperature may be required, such as a thermostatic mixing valve (TMV). Building Regulation ADG3 requires the maximum temperature from a bath tap to be no more than 48˚C.

Secondary returns or maintenance trace heating

Secondary returns or maintenance trace heating is often specified alongside larger systems, where outlets are potentially a significant distance away from the hot water store. This is key to ensuring there is enough hot water at every point of use. For systems incorporating a return, it’s important to keep the circulation temperature above 55°C and to ensure temperature at the hot port of a thermostatic mixing valve (TMV) is above 50°C after one minute of delivery.

Longevity of components

When it comes to choosing components for unvented hot water systems, material choice can play a significant role in their longevity. For example, materials such as higher-grade stainless steels, dezinc resistant brasses and alloy sheathed elements cope well under high pressures and temperatures and should be considered depending on the application.


Finally, when determining the installed position of the tank, an important consideration is the discharge arrangement for the system. According to Building Regulation ADG3, any discharge from an unvented system should be visible at some point and safely conveyed to an appropriate place open to the atmosphere where it will cause no danger to people in or about the building.

Ultimately, there is no ‘one size fits all’ solution for specifying hot water provision in commercial buildings. However, by taking the time to consider all factors at play, specifiers can ensure that hot water systems deliver on performance and efficiency, and meet the safety requirements for the building and end-users for which it is functioning. 16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JULY 2019 Read the latest at:

hen specifying an unvented water heater, there are some key considerations that need to be made which will help ensure a building is equipped with the most appropriate solution.

uHeatrae Sadia’s range of Mulpoint Eco unvented water heaters have been designed for light commercial applicaons. Available from 30 through to 100 litres, this range can serve mulple outlets at the same me, ideal for installaons such as canteens, washrooms and commercial kitchens

One of the

most important consideraons in the specificaon process is water supply

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