Water Heater Temperature - All You Need to Know about It

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Last updated: 
February 28, 2018

The sweet spot for water temperature reduces the risk of scalding but delivers enough hot water for your household demand. Not too hot, and not too cold. Call it the Goldilocks setting! This guide gives step-by-step instruction for adjusting water heater temperature to the optimum setting.

Some manufacturers suggest setting water temperature to 140F. However, 140-degree water causes third-degree burns in three to five seconds. It also increases standby heat loss. Setting the thermostat as low as 100F could mean running out of hot water during peak demand. The U.S. Consumer Product Safety Commission (CPSC) and the Department of Energy agree that 120F offers both safety and reduced energy consumption while providing sufficient hot water.

Water heater on the wall

Steps to Adjusting Water Heater Temperature

Here’s an overview of how to adjust water heater temperature to 120F. Each step is explained fully below. First, you’ll want to find out the current water temperature using a thermometer. If the temperature isn’t where you want it, the next steps will be to locate the thermostat on the water heater and make the necessary change. After waiting for the water heater temperature to adjust, you’ll check it again. The last step is to mark the thermostat dial when the temp is right where you want it.

Step 1: Check the Current Water Temperature

If you have a tank-style water heater, don’t use hot water for 30 minutes before checking the temperature. You want the water completely heated before checking it. Run the tap farthest from the water heater long enough to be sure you’re getting the hottest water possible. Fill a mug, and place a food thermometer’s probe in the water. It might take up to 20 seconds to reach full temperature.

Step 2: Locate the Water Heater Thermostat

There are three common water heater types, and here’s where you’ll find the thermostat for each:

  • Gas tank-style water heater: The thermostat is on the outside of the tank near the bottom of the unit. It’s marked with temperature indicators such as “Very Hot” and/or letters A, B, and C.
  • Electric tank-style water heater: Most electric water heaters have two heating coils, top and bottom, and two thermostats. Each will be found behind a raised cover with one or more screws. Remove the cover and any fiberglass insulation covering the thermostats.
  • Tankless water heater: Most tankless units have the thermostat dial or a digital temperature display on the outside front of the unit.

Step 3: Mark the Current Thermostat Setting

When adjusting the water temperature, you’ll want a reference point for where you started.

  • On gas models, a raised arrow on the non-movable part of the thermostat shows the current setting. On electric models, a post with a slot in it replaces the dial. The settings, often actual temperatures such as “125F”, are printed on the fixed part of the thermostat.
  • On either type, use a dry erase marker to mark the current setting. If you don’t have a dry erase marker, place a small piece of tape on the thermostat, and mark it with a pen or permanent marker.
  • If the thermostat has a digital reading, jot down its current setting.

Step 4: Adjust and Mark the New Thermostat Setting

Many water heater thermostats have five marks on the dial: Hot = 120F, A = 130F, B = 140F, C = 150F and Very Hot = 160F

  • On a gas tank-style water heater, simply turn the dial to your preferred setting or between printed settings.
  • On an electric tank-style unit, insert a flathead screwdriver tip into the slot, and make the adjustment by turning the post.
  • Use the Up/Down arrows on a digital thermostat to make your adjustment.
  • Once you’ve changed the water temperature setting, mark the new point without removing the original mark.

Step 5: Recheck the Water Temperature

The water temperature in a tank-style water heater needs to adjust to the new setting. You can wait 12-24 hours for this to occur, or you can speed the process by running a significant amount of hot water and letting the water heater recover. Be energy-smart by running a dishwasher load or a couple loads of laundry rather than wasting the hot water.

  • Repeat steps 3 through 5 until the water is right where Goldilocks would want it, not too hot and not too cold.
  • Remove any tape you’ve applied, and use a permanent marker to mark your ideal temperature.

Man adjusting valve

A Health Warning and an Energy Saving Tip

While water of 120F is ideal for most households, there’s a slight risk of legionellae bacteria in the warm-but-not-hot water.  The DOE recommends a water heater temperature of 140F for those with “a suppressed immune system or chronic respiratory disease.” If you choose the 140F setting, beware the burn risk, especially to children, the elderly and pets. A word of caution to guests in your home will prevent accidental burns.

While this guide has been about adjusting your water heater’s temperature, we’ll throw in an energy-saving tip too. When you plan to be away from home for more than a day or two, turn your water heater to the lowest setting. If it’s an electric water heater, consider turning it off. Keep in mind you’ll have a short wait for hot water after you get home and turn the water heater on or up.

Adjusting the water heater temperature is definitely a DIY job using these easy steps. In a day or less, you’ll have water everyone can use safely that’s hot enough for laundry and bathing. Sharing this information with others is a great way to help them locate the Goldilocks setting that’s just right for all their household needs.

Images source: depositphotos.com

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