The short answer
For most homes in Northern Virginia, set the water heater to 120°F. Don’t trust the dial, though. Check the water at a faucet with a kitchen thermometer, because the mark on the tank and the water at the tap often don’t match.
The part most people don’t know
The gap between 120 and 140 degrees is the gap between minutes and seconds. The Consumer Product Safety Commission’s tap water scald sheet says most adults get a third-degree burn from 150°F water in two seconds, from 140°F water in six seconds and from 130°F water in thirty seconds. At 120°F it takes about five minutes. CPSC says older people and children under 5 are most at risk, and it urges everyone to set the water heater at 120°F. Shriners Children’s adds that a child’s skin burns at a lower temperature than a teen’s or an adult’s.
This isn’t rare. A study in the journal Injury Prevention, summarized by its publisher, BMJ, counted 52,088 emergency room visits, 7,270 hospital admissions and 110 hospital deaths from tap water scalds in the US from 2016 to 2018. Tap water is about one in four of all scald burns. The same study notes that water heater makers adopted the 120°F preset CPSC recommended back in 1988.
$99 Water Heater Flush
We drain and flush the tank, check the anode rod and test the relief valve, then go through the house's plumbing with photos, included. See the flush
Want your own number before anyone comes out? The water heater estimator prices your house in a few questions.
Your dial probably doesn’t say 120
Plenty of gas tanks don’t show degrees at all. On one A.O. Smith gas water heater, the marks run HOT, A, B, C and VERY HOT, and the manual lists them as roughly 120, 130, 140, 150 and 155°F, with a note that those are approximate. DOE’s Energy Saver guide says plainly that thermostat dials are often inaccurate.
It gets stranger. The same A.O. Smith manual says lots of short draws, like a few hand washes in a row, can make the hot and cold water in the tank stack in layers, and the water at the top can then run as much as thirty degrees hotter than the setting. So a dial set at B can, now and then, send water out of the tap a lot hotter than 140.
How to check yours
- Test first thing in the morning, or at least two hours after anyone used hot water, per CPSC. DOE says use the tap farthest from the water heater.
- Run the hot water and hold a candy or meat thermometer in the stream until the number stops climbing.
- Over 120°F? Turn the dial down a notch and test again the next day. Small steps.
- Electric tank? Most have two thermostats, one behind an upper panel and one behind a lower panel, and CPSC says set both to the same temperature. Turn the breaker off before you open either panel.
Does turning it down save money?
Some. DOE’s guide says some manufacturers set water heaters at 140°F, while most households only need 120°F, which also slows mineral buildup and corrosion in the tank and pipes. At 140°F, DOE says, a water heater can waste $36 to $61 a year just keeping the tank hot. Going away for a while? DOE says turn it to the lowest setting or off.
What about Legionella, the bacteria behind Legionnaires’ disease? DOE says there’s a very slight risk at 120°F, and that the setting is still considered safe for most people. If someone in the house has a suppressed immune system or a chronic lung disease, DOE says you may consider keeping the tank at 140°F, and a mixing valve on the outlet keeps the water at the tap from scalding.
What we check
A tank that rumbles has sediment in it; that’s what Rheem’s own manual lists as the cause. Here’s what sediment does to a water heater. Hot water slow to reach the tap is its own problem: why hot water takes so long. On gas tanks, also know the signs of a backdrafting flue and how long a water heater lasts.
Our water heater flush is $99: we drain and flush the tank, check the anode rod and test the relief valve, then go through the house’s plumbing with photos, included. If the tank is the problem, our water heater estimator shows your installed price first, then $500 comes off a new water heater, any size, replaced by our own plumbers.
Water heater showing a code or a blinking light? Our error codes and warning lights guide covers what each one means.
Book it
Book the water heater flush, call (703) 997-9757, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What temperature should I set my water heater to?
120°F for most homes. CPSC recommends it to prevent scalds, and DOE says most households only need 120°F. Check it at the tap with a thermometer, since dials are often off.
How hot is too hot for a water heater?
CPSC says 140°F water gives most adults a third-degree burn in about six seconds, and 150°F in about two. At 120°F it takes about five minutes, which is why 120 is the number.
What do HOT, A, B and C mean on a water heater?
On one A.O. Smith gas tank, HOT is about 120°F, A about 130, B about 140, C about 150 and VERY HOT about 155. The manual says those are approximate, so check at the tap.
Is 120 degrees safe for Legionella?
DOE says 120°F carries a very slight risk and is still considered safe for most people. With a suppressed immune system or chronic lung disease in the house, DOE says you may consider 140°F with a mixing valve so the tap doesn’t scald.
