Two temperatures for one cylinder of hot water

Two temperatures, in two places

The same cylinder is asked to be hot in one place and cool in another, and the states say so in different words. Victoria’s commission explains the reason: hot water needs to be stored above 60 °C in hot water systems to prevent bacteria growth such as Legionella, but a tempering valve ensures that the water comes out of the tap at a lower temperature. South Australia puts both numbers in one sentence: the delivery temperature must not be higher than 50 °C where the water is used primarily for personal hygiene, and the water needs to be stored above 60 °C to prevent stagnation and bacteria growth such as legionella. Tasmania sets the store as a floor, not a ceiling: the temperature setting for stored heated water must not be less than 60 ºC, to kill off Legionella or other bacteria.

Scald prevention applies to the fixtures people wash at, not to every outlet. NSW’s guidance says heated water must be delivered from the point of discharge at a temperature that is unlikely to scald, and that the state’s scald prevention provision applies to fixtures and appliances used primarily for personal hygiene, including showers, baths, handbasins and bidets. Tasmania makes the same split from the other side: it is not a mandatory requirement to supply tempered water at 50 ºC to a kitchen sink or laundry trough or washing machine taps.

The 50 °C states, named

This part is deliberately narrow. The figure 50 °C is printed here only for the jurisdictions whose own pages state it, and each of those is named with it.

Queensland, WA, the ACT and the NT are not in that table, and 50 °C is not printed for them. None of the pages this guide links from those four jurisdictions states the number.

Queensland names the risk and the work rather than the figure: its legislation puts a hot water service installed in a house without a temperature control device among the risks to an occupier, and the QBCC’s regulated list includes installing or repairing water heaters and tempering valves, so that work is a licensed plumber’s. The ACT puts maintenance in the householder’s year: Evoenergy says to arrange for a qualified gas appliance service technician or gas fitter to service the appliance each year and retain a written report of the work. The Northern Territory is not drawn on here for a figure at all: the NT page this guide can link is about who may do gasfitting work.

Why ten degrees matters

The gap between the two temperatures is a matter of seconds. South Australia prints the burn times beside the limit, under the heading Burn times from hot tap water: at 60 °C it can take just five seconds for an adult, and one second for a child, before third-degree burns occur, while at 50 °C it can take five minutes for an adult or child. The Building and Plumbing Commission reaches the same point from the hot end: at 68 °C, it can take as little as one second to cause a full thickness scald, and at 50 °C it takes five minutes.

Children and elderly people are the reason the exceptions in the table exist: South Australia says children and the elderly are more likely to suffer burns than other age groups, as their skin tends to be softer and they are less likely to be able to protect themselves. The Victorian commission’s safety guide records that more than 90 per cent of hot water scalds to children and elderly or disabled people occur in the bathroom.

The valve behind the mixer, and whose work it is

The part that holds the outlet temperature down is a mixing or tempering valve, and it sits in the copper, behind the wall. Victoria defines a tempering valve as a mixing valve used to temper a hot water supply with cold water to provide hot water at a lower temperature, and a thermostatic mixing valve as one whose mixed outlet temperature is automatically controlled to a preselected temperature suitable for direct contact with the skin. Fitting one is on the licensed side of the line: thermostatic mixing valve work is the repair, alteration, maintenance and testing of a thermostatic mixing valve, and a licensed or registered plumber carrying it out must comply with the standards set out in the regulations.

Tasmania sets the substitution rule between the two kinds of valve: a thermostatic mixing valve may be substituted for a tempering valve, but where an installation requires a thermostatic mixing valve, a tempering valve must not be installed in its place. And whatever device is fitted needs looking after: South Australia says all water temperature control devices need regular maintenance and performance testing. A system installed before the rules changed may not have one at all: the commission says hot water systems installed before 5 August 1998 are unlikely to be tempered, and South Australia says systems installed before 1998 are unlikely to have temperature control devices fitted, with a licensed plumber the person to speak to about fitting one.

One more part is a licensed hand’s, by the drawing’s second ink: NSW’s guidance says a licensed plumber is responsible for ensuring that any heated water services they install, replace, repair or alter comply with the relevant code requirements.

If someone is scalded

First aid is not written out here. A scald is a burn caused by hot water or steam, and the steps for it belong with the health services that publish them: healthdirect’s burns and scalds page and the Better Health Channel’s page on burns and scalds are the two this guide hands you. healthdirect also prints its helpline, 1800 022 222, with a registered nurse available to speak with you 24 hours a day, seven days a week.

Before any of that, the two numbers in this guide’s own table are the ones to hold on to: a stored cylinder above 60 °C to keep Legionella down, and the bathroom outlet held to the maximum your own state’s source sets, 50 °C in Victoria, South Australia and NSW, and 45 °C in the premises the table names.

The cylinder itself

Which system sits behind the mixer changes how the numbers are reached. The national energy site says electric storage systems are used by around 50 per cent of Australian households, are the cheapest to buy and install and generally more expensive to run unless powered by a solar PV system; heat pump water heaters use 30 per cent of the energy of a conventional electric hot water system; and gas water heaters are usually installed outdoors because of venting requirements. Solar and heat pump systems may be eligible for small-scale technology certificates, which can be traded for cash or a discount on the purchase price. Whichever it is, the state rules above apply at the outlet, where the hand meets the water.