The water heater is the appliance most of us meet exactly twice: the day we move in and the day it fails. In between, one setting on it quietly shapes every shower and bath in the house.
The U.S. Consumer Product Safety Commission urges everyone to set water heaters to 120°F. Its reason is scalding. In CPSC’s words, “Most adults will suffer third-degree burns if exposed to 150 degree water for two seconds. Burns will also occur with a six-second exposure to 140 degree water or with a thirty second exposure to 130 degree water.”
- 150°F water: third-degree burns in 2 seconds
- 140°F water: burns in 6 seconds
- 130°F water: burns in 30 seconds
Each ten degrees buys a lot more time to pull a hand away. But CPSC is clear that 120°F is not a magic number either: even at that temperature, a five-minute exposure could cause third-degree burns. The agency says most tap water scald injuries and deaths happen to older adults and children under five. It also notes that turning the temperature down saves energy and money.
While you’re thinking about the tank: sediment from minerals in the water builds up inside it over time. One major water heater manufacturer says most tank water heaters need flushing at least once a year, more often with hard water, and recommends inspecting the “sacrificial” anode rod yearly. That rod is a metal part inside the tank that corrodes on purpose so the tank itself doesn’t. Your own owner’s manual is the final word for your model.
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Try this at home
Measure, don’t guess. CPSC’s method: first thing in the morning, or at least two hours after anyone has used hot water, run the hot tap and hold a candy or meat thermometer under it.
If the reading is well above 120°F, here’s where to stop and hand off:
- Gas water heater: CPSC says thermostats differ, so call your gas company for instructions. Anything involving gas is a job for them or a licensed pro.
- Electric water heater: adjusting it means shutting off the breaker and removing access panels to reach the thermostats. Call your electric company or a licensed pro.
- Apartment: talk to your building manager.
- Hot water from your furnace, not a separate heater: CPSC says to contact your fuel supplier.
Flushing the tank and checking the anode rod also involve gas or electricity and hot water under pressure. If you haven’t done it before, have a licensed plumber do it and watch.
And always hand-test bath water before a child gets in. CPSC adds that a young child should never be left alone in the bathroom, even for a second.
Did you check yours? What did the thermometer say?
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Sources
Everything above is checked against these. Open any of them.
- U.S. Consumer Product Safety Commission, “Avoiding Tap Water Scalds” (Pub. 5098; 120°F; 150°F/2 s, 140°F/6 s, 130°F/30 s, 120°F/5 min; elderly and children under five; thermometer method; gas: call gas company; electric: breaker and access panels; apartment: building manager; hand-test)https://www.cpsc.gov/s3fs-public/5098-Tap-Water-Scalds.pdf
- A. O. Smith (manufacturer), Water Heater Maintenance (flush tank models at least once a year, more with hard water; inspect anode rod yearly; call a professional if not comfortable with gas or electricity)https://www.hotwater.com/info-center/water-heater-maintenance.html
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