What is an efficient temperature for a gas water heater thermostat?

ENERGY STAR recommends setting water heater thermostats to 120 degrees Fahrenheit for efficient operation. This setting can save homeowners up to $30 each year for each 10 degrees of reduction below 140 degrees.

Homeowners with chronic respiratory diseases or suppressed immune systems may still wish to keep the thermostat at 140 degrees, which is a standard used by many manufacturers of water heaters, as it helps reduce or eliminate the risk of legionellae bacteria growth in the water. The United States Department of Energy also recommends insulating the hot water storage tank and installing heat traps on the pipes to help increase efficiency.