Most water heaters have a simple thermostat you can adjust yourself in under ten minutes. The process differs slightly between gas and electric models, but neither requires special tools or a professional. Before you crank things up, though, it helps to understand the tradeoffs between hotter water, energy costs, and burn risk so you land on the right temperature for your household.
Adjusting a Gas Water Heater
Gas water heaters are the easiest to adjust. The temperature control is a dial on the outside of the unit, typically located near the bottom where the gas valve sits. Turn the dial toward a higher setting. Many models display actual temperatures on the dial, while others use labels like “Low,” “Medium,” and “Hot.” If yours uses labels, check the owner’s manual for the corresponding temperatures, since the exact values vary by manufacturer. “Medium” often corresponds to roughly 120°F, and “Hot” can mean 140°F or higher.
After adjusting, wait at least two hours before testing. Run the hot water tap closest to the heater for a minute or two, then check the temperature with a cooking thermometer or an inexpensive probe thermometer held under the stream. This gives you a real-world reading rather than relying on the dial’s accuracy, which can drift over time.
Adjusting an Electric Water Heater
Electric models require a few more steps because the thermostats are hidden behind access panels on the tank. Before you touch anything, shut off the breaker that powers the water heater. This is not optional. The thermostats sit near exposed electrical wiring carrying 240 volts.
With the power off, remove the upper and lower access panels (usually held on by a couple of screws). Behind each panel you’ll find insulation and a plastic safety cover. Pull the insulation aside and remove or flip open the plastic cover to reveal a small white dial. Use a flathead screwdriver to turn each dial to your desired temperature. Most electric heaters have two thermostats, one upper and one lower, and you should set both to the same temperature so the tank heats evenly.
Replace the covers, restore power at the breaker, and wait two to three hours before testing at the tap. Electric heaters recover more slowly than gas, so give the full tank time to reach the new setting before judging the results.
Choosing the Right Temperature
The U.S. Consumer Product Safety Commission recommends setting your water heater to 120°F. At that temperature, the water is hot enough for comfortable showers and effective cleaning, and it takes roughly four to five minutes of continuous skin contact to cause a third-degree burn. That margin of safety matters, especially in homes with young children or elderly residents.
Raising the temperature shortens that safety window dramatically. At 130°F, a third-degree burn can happen in about 30 seconds. At 140°F, it takes only six seconds. At 150°F, just two seconds of contact causes a severe burn. Every 10-degree increase also adds to your energy bill, since the tank has to work harder to maintain and reheat that water throughout the day.
So why would anyone go above 120°F? Two common reasons: your dishwasher requires hotter water for proper sanitizing (some older models without an internal heating element need at least 130°F), or you consistently run out of hot water before everyone in the household has showered. A hotter tank effectively stretches its capacity, since you mix in more cold water at the tap to reach a comfortable temperature.
Why 120°F Is Sometimes Too Low
There’s also a hygiene argument for storing water hotter than 120°F. Legionella, the bacteria responsible for Legionnaires’ disease, thrives in water between 77°F and 113°F and can still survive at temperatures below 120°F. The CDC recommends storing hot water above 140°F to actively suppress Legionella growth, particularly in large buildings or homes where water sits stagnant in long pipe runs.
This creates a real tension: 140°F kills bacteria effectively but poses a serious scald risk at the faucet. The best solution for most households is a thermostatic mixing valve.
Using a Mixing Valve for Safety and Performance
A thermostatic mixing valve (TMV) installs on the hot water outlet of your tank and automatically blends in cold water to deliver a safe, consistent temperature at every fixture. You set your water heater to 140°F for bacterial prevention and greater effective capacity, while the valve blends the output down to 120°F before it reaches your taps.
The performance gain is significant. A 40-gallon tank set to 140°F with a mixing valve can deliver as much usable hot water as a 60-gallon tank set to 120°F, because every gallon of stored water gets diluted with cold water at the valve. You get more showers per tank, better bacterial protection, and safe temperatures at the faucet, all from the same unit. A mixing valve typically costs $50 to $150 for the part itself, and a plumber can install one in under an hour.
Troubleshooting If the Water Won’t Get Hotter
If you’ve turned the thermostat up and the water still isn’t hot enough after several hours, a few things could be going on. On electric heaters, one of the two heating elements may have failed. When the lower element burns out, you’ll get a small amount of very hot water followed by lukewarm or cold water, since only the top portion of the tank is being heated. A multimeter test on each element confirms this, and replacement elements are inexpensive.
On gas units, sediment buildup at the bottom of the tank can insulate the water from the burner, making the heater sluggish and inefficient. Flushing the tank by connecting a garden hose to the drain valve and running it until the water clears can restore heating performance. This is worth doing annually regardless.
A broken dip tube is another common culprit. The dip tube directs incoming cold water to the bottom of the tank. If it cracks or deteriorates, cold water mixes near the top where the hot water outlet sits, diluting every gallon before it reaches your faucet. Replacing a dip tube is a straightforward repair for a plumber and often solves “not hot enough” complaints that no thermostat adjustment can fix.