What is the maximum temperature for a water heater?

When water is being stored in hot water systems , the Plumbing Code of Australia sets rules and regulations around its storage, including its temperature. All systems, including electric, solar, gas and heat pump systems, all must be regulated at a temperature of at least 60°C to stop the growth of bacteria, such as Legionella, which can cause harm to humans.

What is Legionella?

Legionella is a bacterium that can cause Legionnaires disease, which is a severe form of pneumonia. It is formed in damp or wet environments and is not transferred from person to person - it spreads through the mist, such as from air-conditioning units. It is a particularly dangerous illness for people over 50, people with chronic illness, those who smoke, and those with weakened immune systems.

So, what temperature should hot water be delivered at?

Although 60°C is the best temperature for hot water storage in hot water systems, if you had water coming out of your faucets at that temperature it would likely result in scalds. As such, it is recommended that a tempering valve is installed to ensure that the water that comes from the taps is at a much safer temperature of 50°C. A balmy 50°C means that the risk of harm from hot water is noticeably reduced, however, there are exceptions to this :

• Early childhood centres and schools require a thermostatic mixing valve to set the hot water at no more than 45°C
• Nursing homes or facilities which cater for the young, sick, aged, or disabled also require a thermostatic mixing valve to set the hot water at no more than 45°C
• Areas of your home such as the laundry or kitchen may need hot water set at a higher temperature - such as 60°C - to efficiently operate some appliances like washing machines or dishwashers.

Do I need a tempering valve installed?

In order to ensure that the hot water that is delivered in a home is at a temperature that complies with the Australian Standards (AS3500), a tempering valve is required to be installed in all hot water systems in Brisbane. A tempering valve is installed on the water pipe feeding areas of a home to regulate water temperature in personal hygiene areas of the home (like an ensuite). The Standards state that hot water must be regulated at a particular temperature to reduce scalding - 60°C is the accepted temperature for stored water and 50°C for water flowing from an outlet.

Important hot water points to remember

• The water that is being kept in storage for your hot water system must be kept at a temperature of at least 60°C to avoid bacteria growth.
• Ensure you have a tempering valve installed in your home so you can safely maintain the hot water temperature at all times.
• For areas in your home that are used for personal hygiene, such as the bathroom, the temperature of the water coming out of the faucet should be no more than 50° Celsius to avoid harm such as scalds.

If you are unsure as to the hot water temperatures in your home, whether it be in your hot water system or your taps, give us a call on 1300 762 260 and we can arrange for one of our plumbers to come out and check the temperature and install a tempering valve today. Otherwise, contact us online and we can help you with anything to do with your hot water system!

A warning label on a water heater.

Burns are nasty injuries — they're painful and, if you're not careful, they can quickly get infected. Two children die from burn injuries every day, according to the Centers for Disease Control and Prevention. A surprising number of these deaths originate with tap water that is way too hot.

The problem, a new study suggests, is that many water heaters are set dangerously high.

Wendy Shields is a scientist at the Johns Hopkins School of Public Health who studies home injury risks. Shields wanted to look at home water heaters because she says she couldn't understand why tap water burns are still common, causing an estimated 1,500 hospital admissions and 100 deaths per year.

You see, back in 1988, the Consumer Product Safety Commission recommended that water heater manufacturers preset the maximum temperature at 120 degrees Fahrenheit to prevent burns. And the manufacturers voluntarily followed those recommendations — supposedly.

But a lot of people have continued to be scalded by water coming from the shower or tap. "We expected to see a drop off in burns after the old heaters were phased out," Shields tells Shots, "but that hasn't happened."

So Shields and her colleagues surveyed nearly 1,000 homes in Baltimore to find out whether water heaters were actually set at 120 degrees. They found that the heater setting was unsafely high in 41 percent of the homes, including 27 percent with temperatures at or above 130 degrees Fahrenheit.

"This is really dangerous for an older person or a young child," Shields says.

Young children are especially at risk for scald burns because their skin is thinner; the elderly are also at a higher risk because they can be less sensitive to temperature, so may be slower to move away from the scalding water.

The problem in many homes, Shields says, is that most water heaters don't even have a thermostat that adjusts to a specific temperature.

So, to avoid tap water burns, Shields recommends testing your water heater by letting the hot water run from the tap for three minutes, then checking the water temperature with a candy thermometer. "If it's too hot, lower the gauge on the heater," she says. "Then test it a second time to make sure you've really gotten it down to 120 degrees."

The study appears in the March issue of the Journal of Burn Care & Research.

There are two opposing risks when it comes to water temperature inside domestic water heaters; exposure to Legionella, the bacteria responsible for Legionnaires’ disease (pulmonary legionellosis), and the risk of scalding. In 1986, this dilemma was the subject of an editorial in the Canadian Medical Association Journal (1). A few months ago, Safe Kids Canada launched a media campaign aimed at preventing scalding by lowering domestic hot water temperature to 49°C at the tap (2). Among the means considered to reach this objective, Safe Kids Canada, with the support of some public health organizations, suggests and seems to favour lowering the temperature setting of domestic hot water heaters to 49°C.

Like other authors (3,4), including the World Health Organization (WHO) who published a recent monograph on the Legionella problem in drinking water (3), we believe that there is evidence for the transmission of legionellosis through the drinking water distribution systems in private homes. This is a serious illness associated with high death rates (up to 12%). Primary groups at risk (the elderly, smokers, the immunocompromised and patients suffering from chronic respiratory illnesses), are groups who include a large proportion of the population at home. Although we support prevention against tap water scalds, we are against setting water heater thermostats at 49°C because we believe this could facilitate proliferation of Legionella inside the tank and increase the risk of legionellosis.

Domestic water heaters, particularly electric devices, can certainly be contaminated by Legionella. In Quebec, a study of 211 homes (178 electric water heaters, 33 oil or gas water heaters) found Legionella contamination in 40% of electric water heaters. No water heaters using fossil fuels were contaminated (5). The authors concluded that, because of design variables, use of an electric water heater was the most significant factor leading to Legionella contamination in hot water (5) in the home.

The clinical and epidemiological significance of this finding is much debated. However, in a case-control study of sporadic cases of community-acquired legionellosis, Straus et al (6) concluded that the residential drinking water supply was responsible for a substantial proportion of sporadic cases of Legionnaires’ disease. These findings are supported by Stout et al (7) in a study of 20 Pittsburgh patients with culture-confirmed Legionnaires’ disease. A link with residential drinking water contamination was established for eight (40%) patients. This included three private homes (one single dwelling, two multidwellings), two senior-citizen homes, two out-patient hospital clinics, and one industrial plant. The authors concluded that drinking water distribution systems were a significant source of transmission of Legionnaires’ disease (7).

The importance of Legionnaire’s disease is underestimated because it is difficult to diagnose and b ecause it is reported through a passive surveillance system. In an active surveillance study of pneumonia requiring hospitalization in Ohio, the incidence of Legionnaire’s pneumonia was estimated to be approximately seven cases per 100,000 people (8). With the observations from the Stout et al (7) study, if active surveillance was performed, an estimated two cases of Legionnaire’s disease per 100,000 people per year could be attributable to potable water in private homes and senior-citizen residences. This is at least of the same order of magnitude as the annual rates of 0.45 per 100,000 for hospitalization and 0.043 for death due to scalding by tap water in Quebec (9).

The optimal temperature for Legionella proliferation in water varies between 32°C and 35°C, but it can easily proliferate at temperatures of up to 45°C. Usually, there is no growth above 55°C, and a temperature of over 60°C has a bactericidal effect. Thus, the WHO recommends that water be heated and stored at 60°C (3). However, studies in Quebec have shown, even when the thermostat is set at 60°C, a high percentage (approximately 40%) of electric water heaters remain contaminated because of the lower temperature, about 30°C to 40°C at the bottom of the tank. The probability of contamination will increase considerably if the temperature setting is lowered to 49°C. The risk of contamination is much lower for water heaters operating with fossil fuels, and is practically nonexistent for these heaters set at 60°C.

In our opinion, it is important to reduce both the risk of scalds and the risk of legionellosis associated with domestic water supplies (9). For water heaters servicing a single housing unit, electric water heater manufacturers need to market, as quickly as possible, water heaters resistant to proliferation of Legionella. At the least, all new water heaters must be preset at 60°C and equipped with antiscald devices to deliver water at 49°C to the entire household. Electric water heaters already installed should be set at 60°C to limit the risk of Legionella contamination. Gas or oil water heaters already installed should be set at 49°C, because the risk of scalding is greater with these devices. In fact, when there are repeated demands for hot water, gas or oil water heaters are likely to deliver water that is much hotter than the preset temperature, with a greater risk of scalding in some situations (10). Water heaters servicing multiple unit housing complexes equipped with more complex water distribution systems are more likely to be contaminated, and the recommendations from the WHO should apply no matter what type of water heater is used (3). These recommendations state hot water must be stored at 60°C inside the water heater by ensuring, at least once a day, the temperature reaches at least 60°C in the entire tank. Moreover, water should reach the tap at a temperature of at least 50°C. Taps in these buildings, especially in the bath or shower where most scalds occur, should be equipped with antiscald devices to decrease the water temperature to 49°C or less. Such a strategy would minimize the risk of scalding and the risk of legionellosis for the population.

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