Most electric water heaters ship from the factory set to 120°F, and raising the temperature is a straightforward job that takes about 10 minutes with a flathead screwdriver. The thermostat is hidden behind an access panel on the side of the tank, and you’ll adjust it by turning a small dial. Before you start, it helps to understand what temperature you actually want, because the range between comfortable and dangerous is narrower than most people realize.
Choosing the Right Temperature
The U.S. Consumer Product Safety Commission recommends keeping residential water heaters at 120°F to minimize scald risk. That said, there are legitimate reasons to go higher. If your household uses a lot of hot water and runs out quickly, raising the temperature means each gallon carries more heat, so it stretches further when mixed with cold water at the tap. Some dishwashers without internal heating elements also need hotter supply water to sanitize properly.
The CDC recommends storing hot water above 140°F to prevent Legionella, the bacteria responsible for Legionnaires’ disease. Legionella thrives between 77°F and 113°F and can grow at temperatures as low as 68°F. If you have a large tank where water sits for long periods, or if anyone in your home has a compromised immune system, 140°F at the tank is worth considering. You can then install anti-scald mixing valves at individual fixtures to bring the water back down to a safe delivery temperature.
The burn risk at higher temperatures is real and steep. Water at 150°F scalds skin in less than one second. At 140°F, it takes just one second. At 120°F, a scald requires about four minutes of sustained contact. That difference matters enormously if you have young children or elderly family members in the house.
Step-by-Step Thermostat Adjustment
You’ll need a flathead screwdriver, a thermometer (a kitchen meat thermometer works fine), and about 10 minutes. Here’s the process:
- Turn off the power. Go to your home’s circuit breaker panel and flip the breaker that controls the water heater. This is not optional. Electric water heaters run on 240 volts, and the thermostat sits right next to live wiring. If you’re unsure which breaker is correct, flip the one labeled “water heater” or test by running hot water and seeing which breaker kills it.
- Remove the access panel. On the side of the tank, you’ll see one or two metal panels held in place by screws. Remove the screws and set the panel aside. Behind it, you’ll find a layer of insulation (usually fiberglass or foam). Pull it back carefully to expose the thermostat.
- Note the current setting. The thermostat has a small dial with temperature markings. Before you change anything, note where it’s currently set so you can return to it if needed.
- Turn the dial. Use the flathead screwdriver to rotate the dial to your desired temperature. Most dials move in small increments. Turn clockwise to increase the temperature.
- Reassemble. Push the insulation back into place, reattach the panel with its screws, and flip the circuit breaker back on.
- Test after a few hours. The tank needs time to heat up to the new setting. Wait two to three hours, then run hot water at a faucet for about a minute. Fill a cup and check the temperature with your thermometer.
How to Handle Dual Thermostats
Most standard residential electric water heaters have two heating elements, one in the upper half of the tank and one in the lower half, each controlled by its own thermostat. If your heater has two access panels, you have a dual-element system and need to adjust both.
The upper thermostat is the boss. It always fires first, heating the top portion of the tank so you get usable hot water quickly. The lower element doesn’t receive power until the upper thermostat is satisfied. This means the two thermostats play different roles, and setting them identically isn’t always ideal.
A common approach is to set the upper thermostat 5 to 10 degrees higher than the lower one. This distributes the workload more evenly between the two elements, which helps both last longer. If you set them to exactly the same temperature, the lower element ends up doing most of the work to maintain tank temperature, wearing it out faster. Setting the upper significantly higher (say, 150°F up top and 120°F below) gives you a small volume of very hot water quickly but less overall capacity at a consistent temperature.
If you adjusted only one thermostat and your water still isn’t hot enough, check the second panel. This is the most common reason people think the adjustment didn’t work.
When the Problem Isn’t the Thermostat
If you’ve turned the temperature up and your water is still lukewarm or runs out fast, the thermostat setting may not be the issue. A failing heating element is one of the most common causes of underwhelming hot water, and it mimics a thermostat problem almost exactly.
Here’s what to look for. Lukewarm water that never gets truly hot usually means one of your two heating elements has burned out. The remaining element can still heat water, just not enough of it. If you’re getting zero hot water, both elements may have failed, or there’s an electrical issue like a blown fuse or a tripped reset button on the thermostat itself (a small red button you can press to reset). Hot water that runs out much faster than it used to also points to a single failed element struggling to keep up.
Sediment buildup is another culprit. Over time, minerals from your water supply settle at the bottom of the tank and coat the lower heating element. This layer of sediment acts like insulation, preventing the element from transferring heat into the water efficiently. You might hear popping or sizzling sounds from inside the tank as water trapped beneath the sediment layer gets superheated. Flushing the tank annually helps prevent this. If it’s been years since a flush, sediment may have already damaged the lower element.
A water heater that repeatedly trips its circuit breaker often has a short-circuiting or overheating element. This is an electrical problem that won’t be solved by adjusting the thermostat, and the element will need to be tested and likely replaced.
Getting More Hot Water Without Turning Up the Heat
If your real goal is more hot water rather than hotter water, a few other fixes can help. Older water heaters with uninsulated tanks lose a surprising amount of heat just sitting idle. Adding an insulation blanket (available at most hardware stores for under $30) can reduce standby heat loss by 25% to 45%, according to the Department of Energy. That means the water inside stays closer to its target temperature for longer, so the elements cycle on less often and you waste less energy reheating water nobody used.
Insulating the first six feet of hot water pipe leaving the tank also reduces heat loss during delivery. Low-flow showerheads and faucet aerators stretch your hot water supply further by using less volume per minute. These adjustments work alongside a thermostat increase rather than replacing it, but if your household is borderline on hot water capacity, they can make the difference between comfortable showers and cold surprises.