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The water heater installed in your house is big on energy consumption. So naturally, when you think of cutting back on your energy expenses, the water heater’s contributions are one of the first things that come to mind. However, it may not be as simple as dialing the heater’s thermostat back a little; there are a few things that need to be considered first.

Set the temperature too high, and you run the risk of scalding yourself or other members of the household. On the other hand, if you set it too low, you will potentially invite an onslaught of bacteria into your water heater tank. Legionnaires' disease is a form of pneumonia that is transmitted through stagnant water.

This means that if you fail to set the water heater temperature just right, there are two conflicting risks that you can be exposed to:

  • That of scalding from water that is too hot
  • The risk of bacteria and pathogens that will invade the water if the temperature is set too low

How Low Is too Low?

The data provided by the World Health Organization in a paper titled Legionella and the prevention of legionellosis offers a useful insight into how the temperature affects the development and survival of the Legionella bacteria. Below is some information derived from an excerpt from the paper.

  • At temperatures above 70 °C (158 °F), Legionella cannot survive and will die almost immediately
  • At temperatures of 60 °C (140 °F), 90% of the bacteria will die within 2 minutes
  • At temperatures of 50 °C (122 °F), 90% of the bacteria will be killed in about 80 to 124 minutes
  • At temperatures between 48 and 50 °C (118 to 122 °F), the bacteria will survive but will be unable to proliferate
  • Temperatures set between 32 to 42 °C (90 to 108 °F) provide the ideal environment for the bacteria to grow in

Coming back to the question of how low to set the heater temperature, the simple answer is 120 degrees Fahrenheit (50 °C). Most new water heaters come preset at this temperature setting anyway as this corresponds with the temperature recommended by the US Department of Energy. At temperatures close to 50 °C, most Legionnaires’ disease-causing pathogens are killed off and prevented from multiplying. As the temperature gets higher, disease-causing pathogens are terminated quicker. Therefore, agencies such as the Occupational Safety and Health Administration (OSHA) recommend water temperatures as high as 140 degrees Fahrenheit.

It is generally safe to set it at 120 degrees Fahrenheit as per the Department Of Energy’s recommendations. However, if you have people in your house that may have a compromised immune system, it is much better to go for a higher water heater temperature, such as 140 degrees Fahrenheit.

Furthermore, a dishwasher that does not produce its own heat may also compel you to set the temperature in the higher range.

Let’s Talk About the Dishwasher

Most contemporary dishwasher models come with a minimum water temperature requirement of 49 °C (120 °F). They also come with built-in heaters that can heat up the interior as per the washer’s requirements. However, if you have an older version, you should check the specifications to get a fairer idea of what the ideal water temperature is for your dishwasher.

Most dishwater detergents work fine within a temperature range between 50 and 60 °C. There are, however, detergents available on the market that can work at almost any temperature, so you don’t have to be tied to your dishwasher’s needs when deciding on the water heater temperature.

How High Is Too High?

Setting the temperature too high has an obvious risk of scalding while using the water. When you first turn the tap on, you are not immediately exposed to scalding hot water as the water that first comes out is the room temperature (or cooler) water that is already in your pipes. However, the temperature of the water will surely rise, possibly radically, as the water from the heater tank makes its way through the pipes.

Young children are especially at risk of scalding from hot water as their skin is thinner than that of adults. Elderly people too are at a heightened risk of scalding from water that is too hot. Elderly people have skin that is less sensitive, so it will take them longer to realize that the water is hazardously hot for their skin. This is compounded by the fact that the elderly tend to have slower reactions and are slow to respond and move out of harm’s way. This lack of movement, coupled with their reduced sensitivity, means that they’ll be exposed to the hot water for a long time.

At temperatures of 140 degrees Fahrenheit, human skin can receive third-degree burns within five seconds. The fact that it takes a while before the hot water from the heater suddenly pours out from the taps makes going for high water temperatures quite risky.

A Solution

There is a tug of war situation between ensuring scalding safety and pathogenic safety; it almost seems like a difficult balancing act. However, there is an answer to this dilemma: anti-scald valves. Install one of these at each water outlet. This will allow you to set higher temperatures of 140 degrees Fahrenheit while ensuring that it does not go beyond 120 Fahrenheit degrees at the tap.

What about Energy Efficiency Then?

Well, there are other ways that you can cut back on your energy expenses besides dialing the heater’s thermostat back and forth. Try the following:

  • Insulate the hot water pipes.
  • Consume less hot water and cut wastage by taking shorter showers, and by using a dishwasher instead of manual washing.
  • In extreme cases, you can replace your old heater with a newer one that is energy-efficient.

If you feel the need to replace your old heater or need any other plumbing-related assistance around your house, acquire our dedicated plumbing services to take care of all your plumbing needs.

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