What's the Best Temperature for My Water Heater?What's worse than scalding yourself in the shower? Getting Legionnaires' disease—a type of pneumonia carried by stagnant water. Avoid both by setting your water heater to just the right temperature. The DIY experts at Stack Exchange are here to help.

When adjusting my hot water heater, what temperature should I set it to? Is the answer different if you have: concerns about diseases, a dishwasher, young children or elderly that can be easily burned, electric vs. gas heat, type of plumbing (e.g. PEX or Copper)? Also, is there a preferred technique to check the temperature of the water after adjusting it?

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A Goldilocks Water Heater (Answered by SAJ14SAJ)

There are two main and opposing risks:

  • Too high, and users get scalded
  • Too low, and you risk pathogens, particularly Legionella, which causes legionellosis (Legionnaires' disease)

Minimum Temperature

According to the paper Legionella and the prevention of legionellosis, found at the World Health Organization website, temperature affects the survival of Legionella as follows:

  • Above 70 °C (158 °F): Legionella dies almost instantly
  • At 60 °C (140 °F): 90% die in 2 minutes




Maximum Temperature

Setting too high can scald someone using the water. This is particularly easy because when you first open the tap, the water in the pipes has cooled down some, and so its temperature will raise (possibly dramatically) once the water from the tank reaches the point of use. Young children are at higher risk because their skin is thinner. Some people, especially the elderly, are at higher risk because they may be less sensitive and slower to move away from scalding water.The Consumer Product Safety Commission (CPSC) recommends setting to 49 °C (120 °F).

Piping Concerns

What's the Best Temperature for My Water Heater?

From LegionellaPrevention:




Copper in theory would cool down faster than PEX, but given enough time (likely a couple hours), the temperature of both would cool to the ambient temperature. There's a separate question that discusses if it's worthwhile to insulate pipes, but even with insulation, the water in the pipes will eventually cool to ambient.

Conflicting Views



The article Residential water heater temperature: 49 or 60 degrees Celsius?, published in the Canadian Journal of Infectious Diseases, concludes:

"In our opinion, it is important to reduce both the risk of scalds and the risk of legionellosis associated with domestic water supplies. For water heaters servicing a single housing unit: Electric water heaters should be set at 60°C to limit the risk of Legionella contamination, and equipped with antiscald devices to deliver water at 49°C to the entire household. Gas or oil water heaters should be set at 49°C, because the risk of scalding is greater with these devices.

For water heaters servicing multiple unit housing complexes: 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: 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."

The best scenario seems to be to install anti-scald mixing valves at each human point of use (eg, sinks, tubs): whether it be integrated in a shower valve, or installed under the sink. The tank gets set to the WHO-recommended 60°C. Each human point-of-use is limited to the CPSC-recommended 49 °C (120 °F). You may even want it lower (eg, 110 °F) in kid's bathrooms. Other uses—dishwasher, washing machine, humidifier—can get the full 60°C with no issue.


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