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Department of Justice

Heated Water Plumbing

Installation of heated water tempering valves

There are two seemingly conflicting safety issues around heated water temperature

  1. the risk of scalding from heated water
  2. being the risk of incubating bacteria in water that is not hot enough to kill them

Both risks are potentially life threatening, and both can be effectively addressed by complying with the following requirements

  • the temperature setting for stored heated water must not be less than 60ºC to kill off Legionella or other bacteria and
  • a tempering valve device must be installed and set to deliver water to sanitary fixture outlets such as showers, baths, basins, bidettes and bidets and must be set to 50 ºC and
  • for early childhood centres, primary and secondary schools, and nursing homes or similar facilities for the young, aged, sick or disabled persons, a thermostatic mixing valve must be installed and set to 45ºC.

Notes:

It is not a mandatory requirement to supply tempered water (at 50 ºC) to a kitchen sink or laundry trough/washing machine taps.

A thermostatic mixing valve may be substituted for a tempering valve but where installations require a thermostatic mixing valve (see above) a tempering valve must not be substituted / installed.

Point of use heated water heaters must be designed and set to deliver heated water no hotter than 50ºC.

Difference between a tempering valve and a thermostatic mixing valve

A tempering valve is a 3-way mixing valve that is temperature actuated and is used to temper a heated water supply by mixing the heated water with cold water to provide heated water at a lower temperature, normally 50ºC at one or more outlet fixtures.

A thermostatic mixing valve is a mixing valve in which the temperature of the water from the mixed water outlet is automatically controlled by a thermostatic element or sensor to a preselected temperature that is suitable for direct contact with the skin.

Plumbing Code requirements

The Tasmanian Plumbing Code adopts the Plumbing Code of Australia as the standard for plumbing work in Tasmania. This Plumbing Code of Australia requires heated water to be stored and delivered under conditions which avoid the likelihood of growth of Legionella and other bacteria in heated water systems.

This Code also requires heated water supplied by a new heated water service, to be delivered to fixtures and appliances used primarily for personal hygiene at a temperature which reduces the likelihood of scalding. Heated water stored in a hot water storage tank kept at 60ºC or greater will prevent the likelihood of Legionella and other bacteria growth and the installation of a tempering valve or thermostatic mixing valve will reduce the likelihood of scalding.

Installation issues

Some plumbing contractors, in meeting the heated water delivery temperature performance requirement to reduce the likelihood of scalding in the Plumbing Code of Australia are either installing heated water storage units that are factory set to deliver heated water to outlet fixtures at 50ºC or are installing a tempering valve, set at 50ºC, at the outlet of the water heater or the water heater storage tank. Although these methods satisfy the performance requirements for scalding in the Plumbing Code of Australia, they result in controlling the temperature to all fixtures and appliances and not just those used for personal hygiene.

The temperature of the heated water delivered at outlet fixtures varies according to the building use and location of the heated water outlet fixtures. The tempering valve can be located as close as practicable to the storage tank or in line servicing a bathroom or en suite. Restricting temperature to kitchens and laundries is optional and not mandatory by regulation but installation options should be discussed with the building owner as scalding can occur at outlet fixtures in these locations.

Installation and maintenance considerations

  • Only install valves that are certified to Australian Standard AS 4032 Water supply-Valves for control of heated water supply temperatures under the WaterMark Certification Scheme
  • Do not install a tempering valve directly onto a heated water storage tank
  • The pipe work from the water heater to the tempering valve should be copper or copper alloy
  • The pipework from the tempering valve into the building can be of any authorised pipework material
  • Tempered water lines must run at least for one metre from the tempering valve to the fixture outlet
  • Separate un-tempered heated water pipework to the kitchen and laundry
  • Annual check of installed heated water mixing valves to verify the functionality of the valve by a plumber
  • Where the water quality is poor or other supply variations are likely, more frequent monitoring of the valves functionality may be necessary
  • Valves must be installed in positions which are readily accessible
  • At time of commissioning valve, the heated water and cold water pressures should be as equal as practicable
  • Manufacturer's special installation instructions for the valve should be considered before installing or maintaining the valve
  • Do not turn down the thermostat as this could aid in the growth of Legionella
  • Only install water heaters and hot-water storage tanks certified under the WaterMark Certification Scheme to Australian Standard  AS 3498 Authorisation requirements for plumbing products - Water heaters and hot-water storage tanks.

When should tempering valves be installed

The requirement to limit certain heated water temperatures applies to all new heated water installations. A new heated water installation includes: when the water heater and the heated water reticulation are both newly installed; or when a heated water reticulation to a new ablution area is installed.

Therefore, heated water temperature control applies to all new buildings and housing and where the heated water supply piping is being reconfigured such as in addition of an en suite or a bathroom renovation or the installation of an alternate heating system.
However, when work involves only the replacement or servicing of an existing water heater or minor alterations to the heated water piping, there is no requirement to fit a temperature control device to limit the temperature of the water delivered to sanitary fixtures used for personal hygiene purposes.

Legal risks to contractors

Contractors have a 'duty of care' to their customers. Past litigation has placed the onus on plumbing contractors to ensure that heated water installations are safe in domestic situations. This means that because of their professional expertise and qualifications they have the responsibility to ensure that any heated water installation they have worked on is 'safe' and adequate and complies with the Codes. This duty of care includes an obligation to inform customers of the risk of scalding from heated water installations and possible preventative solutions.

For Plumbing regulatory technical advice contact Consumer, Building and Occupational Services.