Most water heaters ship from the factory set to 120°F, but the actual temperature at your tap can drift higher or lower depending on your setup, pipe length, and thermostat accuracy. Adjusting the thermostat is a straightforward job that takes about five minutes, though the steps differ between gas and electric models. The right setting balances three things: enough heat to kill bacteria in the tank, low enough to prevent scalding, and efficient enough to keep your energy bill reasonable.
Choosing the Right Temperature
The Department of Energy recommends 120°F as a good baseline for most households. At that temperature, water is hot enough for showers and dishwashing, and you’ll save 4% to 22% annually on water heating costs compared to higher settings. Every 10 degrees you lower the thermostat trims energy use noticeably.
There’s a catch, though. Bacteria called Legionella thrive in water between 77°F and 113°F and can survive at temperatures up to about 122°F. Growth stops reliably above 131°F, and temperatures above 140°F actively kill the bacteria. The World Health Organization and the CDC both recommend storing water at 140°F (60°C) inside the tank to prevent contamination, especially if water ever sits unused long enough to cool. The CDC specifically advises setting your heater to at least 140°F and using anti-scald devices at the tap to keep the water that touches your skin closer to 120°F.
If you have young children, elderly family members, or anyone with reduced sensation in their skin, scalding risk matters more. Water at 140°F causes a third-degree burn in just 5 seconds. At 120°F, that same burn takes about 5 minutes of continuous contact. A setting of 120°F at the tank with a thermostatic mixing valve is one way to get both bacterial safety and scald protection, but many households without mixing valves simply set the tank to 120°F and accept the tradeoff.
How to Adjust a Gas Water Heater
Gas water heaters have a single temperature dial on the front of the gas control valve, near the bottom of the tank. You don’t need to turn off power or remove any panels. The dial typically has labeled positions rather than exact degree markings. “Warm” or the lowest setting sits around 80°F to 90°F. The letters A, B, and C generally correspond to 130°F, 140°F, and 150°F. “Very Hot” usually means 160°F. A triangle or notch between settings often marks 120°F.
Turn the dial to your chosen setting. That’s it. The new temperature won’t be immediate. Give the heater one to two hours to heat the full tank before testing the water at a faucet.
How to Adjust an Electric Water Heater
Electric models require a few more steps because the thermostats sit behind access panels on the tank itself, and they carry a real electrical hazard.
Start by switching off the breaker that powers the water heater. This is not optional. The thermostats connect directly to 240-volt wiring. Once the power is off, remove the upper and lower access panels on the front of the tank (usually held by one or two screws each). Peel back or push aside the insulation behind each panel to expose the thermostat.
Electric water heaters typically have two thermostats, one upper and one lower, each controlling its own heating element. The upper thermostat has priority: it heats the top of the tank first, then hands off power to the lower thermostat to heat the bottom. Both should be set to the same temperature. If the lower is set higher than the upper, the lower element will never fully satisfy its thermostat, and you’ll get inconsistent hot water.
Each thermostat has a small dial or a flat-head screw you turn with a screwdriver. Markings are printed on the face, usually in 10-degree increments. Turn both to your target temperature, press the insulation back into place, reattach the panels, and flip the breaker back on. Wait one to two hours before testing.
How to Check the Actual Temperature
Thermostat dials are not precision instruments. The number on the dial and the temperature at your faucet can differ by 10 degrees or more, especially on older units. Always verify with a thermometer before and after making changes.
Pick the faucet closest to your water heater (shorter pipes mean less heat loss). Turn on the hot water and let it run for about two minutes to flush out cooled water sitting in the pipes. Hold a cooking thermometer or a standard digital thermometer under the stream and note the reading. If it’s not where you want it, go back to the thermostat, nudge it a few degrees, wait another hour or two, and test again. It can take two or three rounds to dial in the exact temperature you’re after.
What the Dial Markings Mean
Gas water heater dials are notoriously vague. If yours has letters instead of numbers, here’s a general guide:
- Low / Warm: 80°F to 90°F (not recommended for regular use)
- Hot / Triangle mark: approximately 120°F
- A: 130°F
- B: 140°F
- C: 150°F
- Very Hot: 160°F
These are approximate. Manufacturer calibration varies, which is why testing at the faucet matters more than trusting the label.
Special Situations That Affect Your Setting
Dishwashers without a built-in heating booster need incoming water at 130°F to 140°F to sanitize properly. If yours has a booster (most modern models do), 120°F from the tank is fine.
Long pipe runs between the heater and distant bathrooms can drop the temperature 10 degrees or more by the time water reaches the faucet. If your farthest bathroom consistently runs lukewarm, raising the tank temperature a few degrees may be easier than insulating every pipe. You can also wrap exposed hot water pipes with foam insulation sleeves to reduce heat loss.
Homes where the water heater sits idle for days, like vacation properties, face a higher risk of bacterial growth. In those cases, setting the tank to 140°F is worth the extra energy cost. When returning after a long absence, let the heater run at full temperature for several hours before using the hot water.
Preventing Scalds at Higher Settings
If you set your tank to 140°F for bacterial protection, you’ll want something between the tank and your skin. Thermostatic mixing valves install at the water heater’s outlet and blend cold water in automatically to deliver a safer temperature (typically 120°F) to every faucet in the house. Point-of-use anti-scald valves can also be installed at individual faucets or showerheads. Both are inexpensive and widely available at hardware stores.
This approach gives you the best of both settings: hot enough inside the tank to prevent Legionella, cool enough at the tap to prevent burns. It’s the setup the CDC recommends for buildings where both risks matter.