Top three considerations for specifying TMVs

Specifying plumbing and heating systems for new build developments – whether homes, a hospital or a commercial building like an office block – requires building design specialists to navigate various complexities to create buildings and systems that are suitable for their occupants and the intended use.
One way in which safety is prioritised is through specifying TMVs (Thermostatic Mixing Valves) for plumbing systems. Successful specification of these water control valves comes down to careful planning and consideration.
In this blog, we explore three key considerations for plumbing and heating specifiers to keep in mind to ensure the long-term success of systems using TMVs.
The purpose of TMVs
Firstly, it’s important to understand why TMVs are used in plumbing systems and what purpose they serve when installed and maintained correctly.
TMVs allow for hot water to be stored at high enough temperatures to help prevent against harmful bacteria growth, while blending hot and cold water to ensure safe temperatures at the point of use. In practice, that means water is safe to use, while the potential for users to scald themselves is eliminated.
These benefits are vital in almost every type of building. In domestic environments, for example, they can keep taps, baths and showers at safe-to-use temperatures for people of all ages. TMVs are also used broadly in commercial and healthcare environments – from schools and offices through to hospitals and care homes. In these applications, safety is even more important, with people of all ages and with varying degrees of vulnerability using the water supply.
For more than a decade, TMVs have been a legal requirement in all commercial and domestic new build properties, in addition to properties undergoing a change of use. However, while they are a legal requirement on many projects, when specifying TMVs it isn’t always straightforward to select the most appropriate TMV for the job, with various options supporting compliance in different environments.
Application
The most critical step in specifying TMVs is understanding the requirements of the building you’re working on. Generally, TMVs are split into two groups – TMV2 and TMV3 schemes. These different categories of Thermostatic Mixing Valves indicate the levels to which they perform, directly supporting compliance with regulations that differ by application.
TMV2 valves are typically used in domestic and commercial applications and are required to maintain safe and stable water temperatures up to 48°C. Importantly, valves in this category will also shut off in the event of hot or cold water failure as they will no longer be able to sufficiently mix the supply to a safe temperature. TMV2 valves also allow for group mixing to multiple outlets from a single TMV. These ‘group’ mixing valves are larger than a standard TMV and produce higher flow rates to ensure optimal performance.
Healthcare settings are where TMV3 valves must be specified for use on every water outlet identified within a risk assessment specific to the property in question. Aligned with the requirements outlined in the NHS’s D08 specification, TMV3-approved valves are approved for a period of five years, ensuring they perform as required to prioritise user safety at every point of use. Importantly, it is essential that only a single outlet is served by this type of valve, with no group mixing allowed in the scheme.

Size
Alongside the application where the TMV is being specified, it is also important to consider the sizing of the valves being used.
As with any valve used within a plumbing system, TMVs have a direct impact on the flow of water, helping to manage flow rates across a system and, specifically, towards individual outlets. A TMV that is too large or too small for its intended use can compromise system performance, impacting flow rate, flow pressure and the number of outlets the valve is able to serve. Alongside these factors, incorrect specification can also compromise the fundamental role of TMVs – maintaining safe temperatures.
When specifying TMVs, specifiers need to understand the purpose of the individual valve – such as the number of outlets it will serve. While it may be tempting to specify a larger valve than necessary, this can lead to more water being drawn through, ultimately leading to water wastage. On the other hand, a valve that is too small will result in an inadequate flow rate and insufficient volumes of hot water reaching every outlet.

Maintenance
Just as specification requirements differ by application, so do maintenance needs. In all cases, it is best practice to ensure that TMVs remain accessible, allowing for easy servicing and maintenance when required.
Since TMV3 solutions are designed for healthcare environments, specifiers can safely assume that regular servicing of these valves is especially critical. The TMV3 scheme requires rigorous testing of these valves, starting with an initial service six weeks after installation, followed by testing every six months thereafter.
In environments where TMV2 solutions have been specified, annual servicing is required. This is done by measuring the mixed water temperature, followed by shutting off the valve – replicating what would happen should the cold water supply fail. In this instance, no more than 120ml of water should be supplied to the outlet in a one minute period.
To specify the right TMV for your project, explore the Reliance Valves range of TMVs that has solutions for domestic, commercial and healthcare applications – including with TMV2 and TMV3 approvals.
TMV eGuide
If you’ve found this mini guide to specifying TMVs helpful, check out our eGuide exclusively for specifiers.