How to Set the Right Water Heater Temperature
Updated February 25, 2026
Adjust your water heater to the ideal temperature for safety, efficiency, and bacteria prevention -- covers gas, electric, and tankless models.
Overview
Most water heaters ship set to 140°F. Most households should run at 120°F. That 20-degree difference matters: 120°F reduces scald risk (especially for kids and elderly), cuts energy costs by 6-10%, and slows mineral buildup in the tank. But there is a reason not to go below 120°F -- Legionella bacteria thrive between 77°F and 113°F. Below 120°F, your tank becomes a breeding ground. The sweet spot is 120°F for most homes, 130-140°F if you have a dishwasher without a built-in heater or immunocompromised household members.
What You'll Need
Safety First
- Water at 140°F causes a third-degree burn in 5 seconds. At 120°F, it takes 5 minutes. If you have young children or elderly family members, 120°F and an anti-scald mixing valve at the faucet is the safest setup.
- Do not set below 120°F. Legionella bacteria (causes Legionnaires' disease) grows in water between 77°F and 113°F. A tank sitting at 110°F is a health risk.
- Electric water heaters have TWO thermostats -- upper and lower. Both must be set to the same temperature or the water stratifies unevenly.
Step-by-Step Instructions
- Check the Current Temperature
Run the hot water faucet closest to the water heater for 2-3 minutes until it is as hot as it gets. Hold a cooking thermometer or instant-read thermometer under the stream. That is your actual output temperature. The dial on the heater is approximate at best -- the thermometer gives you the real number.
Tip: The factory setting of 140°F is stamped on most gas valves as the middle position. But dials are notoriously inaccurate. Always verify with a thermometer. Your thermostat dial saying 120 does not mean the water is 120. - Adjust a Gas Water Heater
The gas control valve on the front of the heater has a temperature dial. Turn it to the desired setting. Most dials use letters (A, B, C) or ranges (WARM, HOT, VERY HOT) instead of exact degrees. General mapping: A/WARM = ~120°F, B/HOT = ~130°F, C/VERY HOT = ~140°F. Adjust, wait 2-3 hours for the tank to stabilize, then re-test at the faucet with a thermometer. Adjust again if needed.
Tip: Newer Honeywell gas valves have a dial with actual degree markings. Older Robertshaw valves use the letter system. Either way, verify with a thermometer -- the dial is a starting point, not a guarantee. - Adjust an Electric Water Heater
Turn off the breaker. Remove the upper and lower access panels (usually two Phillips screws each). Pull back the insulation. Each thermostat has a small dial or screw adjustment. Use a flathead screwdriver to set both to the same temperature. Upper and lower must match -- if the upper is set higher, only the top of the tank heats fully. Replace the insulation, panels, and turn the breaker back on. Wait 2-3 hours and test at the faucet.
Tip: The upper thermostat is the master. It heats the top of the tank first, then transfers control to the lower element. If the upper is set to 120°F and the lower is set to 140°F, the lower never reaches 140°F because the upper cuts power before it gets there. Match them. - Adjust a Tankless Water Heater
Tankless units have a digital display or buttons on the front panel. Press the up/down arrows to set the desired output temperature. Most tankless units allow 1-degree increments from 100°F to 140°F. Set to 120°F. The unit heats water to exactly that temperature on demand -- no tank, no stratification, no guesswork. Verify at the faucet, but tankless units are significantly more accurate than tank thermostats.
Tip: Some tankless models allow different temperature presets for different uses. Setting the unit to 120°F for general use and bumping it to 130°F for dishwashing is possible on Rinnai, Navien, and Noritz models with recirculation or multi-set features. - Consider a Thermostatic Mixing Valve
Want the best of both worlds? Set the water heater to 140°F (kills bacteria, maximizes hot water volume) and install a thermostatic mixing valve at the heater outlet ($50-$100). The valve blends cold water in to deliver 120°F to the house. The tank stays hot enough to prevent Legionella, but the water at your faucets is safe from scalding. Plumbers install these routinely -- 30-minute job.
Tip: This is the recommended approach for households with young children, elderly members, or immunocompromised individuals. Hospital and nursing home codes require mixing valves for exactly this reason.
Pro Tips
- Every 10°F reduction in water heater temperature saves 3-5% on water heating energy costs. Dropping from 140°F to 120°F saves roughly $30-$60/year depending on your energy rates and usage.
- Dishwashers made after 2010 have built-in heaters that boost water to sanitizing temperature (140°F+) regardless of your tank setting. Check your dishwasher manual -- you may not need your tank above 120°F at all.
- If you leave for vacation, turn the gas valve to PILOT (gas) or set the thermostat to the lowest setting (electric). No reason to heat 40-80 gallons of water nobody is using. Some units have a VACATION mode that does this automatically.
- Heat pump water heaters in heat-pump-only mode heat more slowly. If you set the temperature to 140°F with a mixing valve, the heat pump may run in hybrid mode more often, reducing your efficiency gain. Set heat pump units to 120°F and skip the mixing valve unless you have a specific need.
- Recirculation systems keep hot water in the pipes at all times. If you have one, setting the heater to 120°F is even more important -- constantly circulating 140°F water wastes energy and accelerates pipe corrosion.
When to Call a Pro
You do not need a plumber to adjust the temperature. Call a plumber if you want a thermostatic mixing valve installed ($50-$100 for the valve plus $100-$200 labor), if your electric thermostat is damaged or the adjustment screw is stripped, or if the temperature does not change after adjusting (may indicate a failed thermostat or gas valve).
Frequently Asked Questions
When should I call a plumber to set the right water heater temperature?
You do not need a plumber to adjust the temperature. Call a plumber if you want a thermostatic mixing valve installed ($50-$100 for the valve plus $100-$200 labor), if your electric thermostat is damaged or the adjustment screw is stripped, or if the temperature does not change after adjusting (may indicate a failed thermostat or gas valve).
What are some expert tips to set the right water heater temperature?
Every 10°F reduction in water heater temperature saves 3-5% on water heating energy costs. Dropping from 140°F to 120°F saves roughly $30-$60/year depending on your energy rates and usage. Dishwashers made after 2010 have built-in heaters that boost water to sanitizing temperature (140°F+) regardless of your tank setting. Check your dishwasher manual -- you may not need your tank above 120°F at all. If you leave for vacation, turn the gas valve to PILOT (gas) or set the thermostat to the lowest setting (electric). No reason to heat 40-80 gallons of water nobody is using. Some units have a VACATION mode that does this automatically. Heat pump water heaters in heat-pump-only mode heat more slowly. If you set the temperature to 140°F with a mixing valve, the heat pump may run in hybrid mode more often, reducing your efficiency gain. Set heat pump units to 120°F and skip the mixing valve unless you have a specific need. Recirculation systems keep hot water in the pipes at all times. If you have one, setting the heater to 120°F is even more important -- constantly circulating 140°F water wastes energy and accelerates pipe corrosion.
What tools do I need to set the right water heater temperature?
You will need: Cooking or instant-read thermometer (to verify actual water temperature), Flathead screwdriver (for electric water heater thermostat adjustment), Phillips screwdriver (to remove electric heater access panels).
When should I call a professional instead of doing this myself?
You do not need a plumber to adjust the temperature. Call a plumber if you want a thermostatic mixing valve installed ($50-$100 for the valve plus $100-$200 labor), if your electric thermostat is damaged or the adjustment screw is stripped, or if the temperature does not change after adjusting (may indicate a failed thermostat or gas valve).
How difficult is this project?
This project is rated easy. Most homeowners with basic tools can complete it.
How long does this take?
Plan for approximately 5 - 15 minutes. First-timers may need extra time.
How much will this cost?
The estimated cost is $0. Costs vary by location and materials chosen.