What Temperature Should a Water Heater Be Set At? 120°F, and When to Go Higher

Set most home water heaters to 120°F. The Department of Energy, ENERGY STAR and the Consumer Product Safety Commission all name that setting because it limits scalds and wasted heat. A higher setting of 130–140°F is mainly a health decision. CDC says it can kill germs like Legionella, but water that hot can burn an adult in seconds, so it belongs with mixing valves at the taps.

The short answer for your household

DOE’s Federal Energy Management Program puts it in one line:

For most residential applications, set the temperature at 120°F.

ENERGY STAR’s home-saving guide says the same, and adds that most water heaters are set at 140°F, which wastes energy through standby heat loss.² The exceptions in official guidance are specific, and each comes with a caution:^3,4,5,7,10

What DOE, CDC, CPSC, EPA and OSHA actually say

The numbers differ because the audiences differ: the 120°F figures are for homes, while most 140°F figures come from Legionella control in large buildings and workplaces.

• CPSC urges everyone to lower water heaters to 120°F, noting that most tap water scald injuries and deaths happen to older adults and children under five.³
• CDC says a home heater at 130–140°F can kill germs like Legionella but raises the burn risk; above 120°F, it advises thermostatic valves that mix hot and cold water at the tap.⁴
• EPA says Legionella grows best at 80–120°F, that a thermostat at or above 140°F can often keep plumbing above 124°F, and that water at the tap can scald above 117°F. It also says to check state and local codes before raising the setting.⁸
• OSHA writes for workplaces and multi-family buildings: water heaters kept below 140°F that contain scale and sediment may foster Legionella growth, and its design examples include keeping hot water lines at 122°F or more.⁹ Some home guides cite this as an OSHA “minimum” for your tank; OSHA’s page describes building systems, not a home setting.
• The Department of Defense requires its service water heaters to store water at 140°F or more, with a tempering valve downstream that FEMP says to set at 120°F in residential use.¹

Factory settings vary too. Against ENERGY STAR’s 140°F,² A. O. Smith says its current heaters come preset at 120°F;¹² and A. O. Smith’s gas-control technical bulletin says the dial ships at its lowest setting unless state rules say otherwise.¹¹ Don’t assume: measure.

How fast hot water burns

Scald risk climbs steeply with each 10°F. CPSC’s tap water scald sheet puts it simply:

Never take hot water temperature for granted.

Most adults suffer third-degree burns after about five minutes at 120°F, 30 seconds at 130°F, six seconds at 140°F and two seconds at 150°F.³ A. O. Smith’s table puts 140°F at “less than 5 seconds”; the two tables agree within a second or two.¹¹

The dial is also less exact than it looks. A. O. Smith’s gas-control bulletin gives each setting a tolerance of ±10°F, and warns that short, repeated heating cycles from small hot water draws can push the water at the tap up to 30°F above the setting.¹¹ That bulletin also explains the letters many gas dials use:

When a hotter setting makes sense: Legionella

Legionnaires’ disease is a serious pneumonia caused by breathing in mist that contains Legionella bacteria, for example from a shower. CDC says the bacteria grow best at 77–113°F, may grow as low as 68°F, and thrive where water sits still, disinfectant runs low, or sediment and biofilm build up.^5,7 Most healthy people exposed don’t get sick. CDC lists those at higher risk: people 50 or older, current or former smokers, and people with chronic lung disease, cancer, diabetes, kidney or liver failure, or a weak immune system.⁶

For homes, CDC’s advice is a conversation, not a number:

Ask your healthcare provider about your risk of getting sick from Legionella

CDC then suggests discussing whether 130°F or above is right for you.⁴ DOE’s Energy Saver page described the risk at 120°F as very slight and safe for most people, and suggested 140°F for someone with a suppressed immune system or chronic respiratory disease, with mixing valves on taps used for washing or bathing.¹⁰ CDC also recommends regular flushing as the manufacturer directs, and notes that many manufacturers advise it yearly and after plumbing work.⁴

Mixing valves: what the sources describe

A thermostatic mixing valve blends cold water into hot so the tap delivers a steady, lower temperature. EPA says to place them as close as possible to the outlets and to follow the maker’s instructions or have a professional install them.⁸ CDC’s building toolkit says valves near fixtures prevent scalding while circulating hot water stays above 120°F.⁷ A. O. Smith adds that the valves can increase the amount of usable hot water.¹²

What turning 140°F down to 120°F saves

DOE’s Energy Saver page, now offline, said a heater set at 140°F can waste $36 to $61 a year in standby heat loss, put the savings at 4%–22%, and said savings on the hot water you use may amount to more than $400.¹⁰ It did not show the math, so here is how the parts work, using only the federal test’s own constants.¹³

• Standby loss roughly follows the gap between the tank and the room. At the test’s 67.5°F room, 140°F leaves a 72.5°F gap and 120°F a 52.5°F gap: about 28% less heat leaking out of the tank.
• Water used straight from the tank (a washer’s hot fill, a dishwasher without a heater) takes 8.24 Btu per gallon for every degree of rise. Cutting the rise by 20°F saves 22–35% of that energy in our 12 cities, more where tap water is warm. A. O. Smith’s “nearly 25% less energy,” which assumes 60°F cold water, is the same arithmetic.¹²
• Mixed water (showers, baths, sinks) saves almost nothing: you still mix the shower you like, so a hotter tank only means less hot and more cold in the same mix.

EPA notes that a setting at or above 140°F may raise your energy use, and suggests insulating pipes to limit the extra loss.⁸

Why your hot water runs out sooner in winter

No source we found recommends a different setting for winter. What changes is your tap water. We estimated each city’s incoming water temperature month by month with the mains-water model in DOE’s Building America House Simulation Protocols,¹⁴ using NOAA’s 1991–2020 climate normals for the station nearest each ZIP code,¹⁵ the same numbers behind our tankless vs. tank water heater guide. The colder the incoming water, the more of each 110°F shower must come from the tank.

*At each city’s yearly average tap water temperature. Higher settings need thermostatic mixing valves at the taps (see above).

In Fargo in February, about 88% of a 110°F shower comes from a 120°F tank, so each stored gallon makes only 1.14 gallons of shower water; in Miami in January it makes 1.30. Raising the tank to 140°F stretches each gallon about 24% further in Fargo and 46% in Miami, which is the capacity gain A. O. Smith describes, but only with mixing valves at the taps.¹²

How to check your temperature without opening anything

1. Wait until hot water hasn’t been used for at least two hours, or test first thing in the morning, as CPSC suggests.³
2. Run hot water at the tap farthest from the heater and hold a cooking thermometer in the stream; DOE notes that thermostat dials are often inaccurate.¹⁰
3. Compare with your target. If you change the setting, re-measure a couple of hours later; several rounds may be needed.¹⁰

We don’t give adjustment steps. On an electric tank the thermostats sit behind access panels, where A. O. Smith warns of electric shock, and on a gas tank the dial is part of the gas control valve.¹² Follow your owner’s manual, or have a licensed plumber make the change and check the result. On a tankless heater, which stores no water, the setting mainly changes winter flow: see our tankless winter flow table.

Next step

Measure your hot water at the farthest tap tonight. If it reads well above 120°F and no one at home needs a hotter tank for health reasons, ask a plumber to bring it down. If someone does, talk to their healthcare provider first and plan for mixing valves. More in our water heater guides and the home energy section. The generator size calculator shows what an electric water heater adds to an outage load, and our methodology page explains how we match ZIP codes to NOAA stations.