Recommended Temperature Settings for Hot Water Heaters

Although manufacturer's usually set water heaters at 140 degrees F, you can reduce your carbon footprint and save money by adjusting your water heater thermostat. According to the U.S. Department of Energy, for each 10 degree reduction in water temperature, you can save between 3 and 5 percent in energy costs. They also recommend setting water heater temperature to 120 degrees F at the faucet to reduce the danger of scalding.

Man checking water heater
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Checking a water heater.

Legionnaires’ Disease

Gauge pressure.
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Manometer.

Inhaling water vapor contaminated with Legionellosis bacteria causes pneumonia-like symptoms that can kill you if left untreated. The Occupational Safety & Health Administration (OSHA) recommends a setting of 140 degrees F in hotels and large systems to control Legionnaires' Disease. However, there is less danger of bacterial growth in smaller domestic hot water tanks. Consequently, OSHA recommends the minimum water heater outlet temperature in residential systems to be set at 130 degrees F to produce a faucet temperature of at least 120 degrees F.

Test Your Water Temperature

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Test water.

Water heater thermostats are not very accurate, and as indicated above, there is some heat loss between the heater and the faucet. Place a deep glass under the hot water tap farthest from the heater. Run the water for a minute or two to heat up the pipes and the glass. When the water reaches maximum temperature, drop a cooking thermometer into the glass to get an accurate reading. Reduce the thermostat setting on your water heater by the appropriate amount. For example, if the delivery temperature is 128 degrees F, lower the thermostat by 8 degrees F.

Set Your Thermostat

Thermostat, close-up
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Thermostat gauge.

Electric storage-tank-type hot water heaters are often fitted with two thermostats -- one at the top, and one at the bottom of the tank. Turn the power to the hot water heater off by tripping the relevant breaker switch on your home's electrical panel. Remove the upper and lower metal inspection covers with a screwdriver and push the insulation aside to reveal the thermostats. Insert a flat screwdriver into the screw surrounded by a temperature dial and adjust it to the desired setting. Replace the inspection plates and restore the power. Gas water heaters are usually fitted with an exposed adjustable knob, but this could also be hidden behind an inspection plate. Turn the knob until the arrow points to the desired temperature. Drain off some hot water to get the heater working again, and retest the faucet temperature after an hour.