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What Temperature Should a Hot Water Heater Be Set at?

Fact checked by Stephen Conklin

what temperature should a hot water heater be set at

Are you like many people wondering what temperature should a hot water heater be set at? Setting the water heater to the ideal temperature is crucial for ensuring not only more pleasant showers. It also safeguards people against diseases.

This article answers your most incessant questions related to the ideal hot water temperature. We will also look at some factors you must consider when setting the heater’s thermostat.

Let us begin.

Table of Contents

What is the Ideal Temperature Setting of a Water Heater?


Two schools of thought exist, shedding light on the question, what temp should a water heater be set at?

Water heater manufacturers set their water heater temperature at 140 degrees Fahrenheit by default, believing most people find the temperature more relaxing and soothing.

The Occupational Safety and Health Administration supports this water heater setting, highlighting the need to prevent the growth and proliferation of Legionella and other pathogenic microorganisms.

According to the Mayo Clinic, Legionella exists in water and soil as non-infectious agents. However, these microorganisms can turn pathogenic when they proliferate in water systems, including air conditioning units and residential plumbing.

Legionella causes infection when people inhale water droplets with the bacteria during showers or when using whirlpools, hot tubs, water heaters, and hot water tanks.

On the other hand, the US Department of Energy and the Environmental Protection Agency set the ideal water temperature at 120 degrees Fahrenheit.

Medical and healthcare experts also weighed in on the debate, recommending that the hot water heater temperature setting must not be lower than 120 degrees Fahrenheit to prevent microbial growth.

Further muddling the answer is the stance of the Consumer Product Safety Commission, recommending a maximum water temperature of 120 degrees Fahrenheit for safety reasons. The organization believes that hot water (higher than 120 degrees) can cause burn injuries in susceptible people.

Most people might consider the 120-degree Fahrenheit recommendation ideal for their family. Unfortunately, no two families or households are exactly alike. That is why it would be best to consider how certain factors play into the equation.

What Factors Should You Consider When Setting the Water Heater’s Thermostat?


People have different perceptions about what constitutes the ideal hot water temperature. I may be comfortable with 120 degrees, but you or other people might prefer 130 or 140 degrees. Regardless of the water heater type you have, it would be best to consider the following factors.


According to the American Burn Association, children below 16 years account for twenty-six percent of admissions to burn treatment centers.

The organization says that younger children are more prone to scalding injuries because of their immature cognitive and motor skills and insufficient parental supervision when using hot water. Young kids also do not have the skills for self-rescue.

The elderly are also susceptible to hot water-related burn injuries because of pre-existing medical conditions, delayed reaction time, and impaired mobility.

Both youngsters and old people also have thinner skin layers compared to other age groups. They can suffer from deeper burn injuries even with short hot water exposure or low water temperature.

The ABA also said that three seconds of exposure to 140-degree Fahrenheit water are all it takes to cause serious burn injury, requiring surgery.

Hence, you might think that a 140-degree Fahrenheit hot water heater setting is safe for you. However, if you have youngsters or elderlies in your family, you must dial the thermostat down to 120 degrees Fahrenheit.

Immune System Functioning

We need a fully functioning immune system to protect us against infections. When an organism invades our bodies, the immune system mobilizes its army of defender cells to fight.

Immunocompromised persons no longer have a formidable defensive army in their bodies, making them susceptible to infections. People with reduced immune system functions may need higher water temperatures to kill microorganisms.

People taking immunosuppressant medications cannot ward off infections. Examples of immunosuppressive agents include corticosteroids, monoclonal antibodies, biologics, and calcineurin inhibitors. The same is true for people with HIV/AIDS, psoriasis, Crohn’s disease, rheumatoid arthritis, and lupus.

Patients undergoing organ transplant procedures also have weakened immune systems, making them more vulnerable to infections.

The ideal temperature for domestic hot water in households with immunocompromised persons is 140 degrees Fahrenheit.

While some microorganisms are thermophilic or heat-resistant, most cannot withstand 140-degree Fahrenheit heat. Even the dreaded Legionella will die at 122 degrees Fahrenheit. Unfortunately, some heat-resistant viruses require more than 140 degrees Fahrenheit for inactivation.

Regardless, setting the water heater temperature to 140 degrees Fahrenheit is sensible for families with immunocompromised members.

Energy Consumption

The US Department of Energy says that setting the water heater to 120 degrees Fahrenheit can generate energy savings between 4% and 22% annually. The savings result from lower demand losses (at least $400 per year) and reduced standby losses (between $36 and $61 every year).

Hence, if you are conscious about your electric bills, you might want to set the water heater to not more than 120 degrees Fahrenheit.

Of course, if budget is not a concern, you can always dial up the thermostat to 140 degrees.

Again, I urge you to consider your family members’ age and immune status to determine the best possible water heater setting.

Water Appliances’ Energy-efficiency

Some dishwashers do not have a ‘water preheat’ function that allows users to dial the water heater thermostat setting to a lower temperature. If you have such a dishwasher, you have no choice but to set the water heater to 140 degrees Fahrenheit.


You have two answers to the question “what temperature should a hot water heater be set at?”

  • Set the water heater to 120 degrees Fahrenheit if you want better energy savings or if you have elderly or young children in the family.
  • Program the water heater’s thermostat to 140 degrees Fahrenheit if your family has immunocompromised members or does not mind paying a hefty electric bill. You might also need this setting if you have a dishwasher without a preheat function.

Deciding on the ideal hot water temperature rests on your understanding of the various factors for

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