A hot water heater provides heated water for daily needs. Determining the ideal temperature setting involves balancing comfort, safety, and efficiency.
The Standard Recommendation
The U.S. Department of Energy and many safety organizations generally recommend setting a hot water heater to 120°F (49°C). This temperature provides sufficient heat for common tasks like bathing, laundry, and dishwashing. This setting also reduces the risk of scalding injuries and discourages harmful bacterial growth within the tank.
This temperature offers a practical middle ground, addressing both safety concerns and energy consumption. While some manufacturers may set units higher by default, adjusting to 120°F (49°C) can be beneficial. It allows for effective hot water use without unnecessary energy expenditure or excessive heat.
Protecting Against Scalds
Hot water can cause severe burns, with the risk increasing significantly at higher temperatures. Water at 140°F (60°C) can cause a third-degree burn in five seconds. Even quicker, 150°F (66°C) water can result in third-degree burns within two seconds. Lowering the water heater temperature helps reduce the speed and severity of potential scald injuries.
Vulnerable individuals, such as infants, young children, the elderly, and those with disabilities, are particularly susceptible to scalds. Their skin is thinner and more sensitive, meaning they burn more quickly. For instance, at 120°F (49°C), it takes approximately five minutes of exposure to cause a third-degree burn, providing a much larger margin of safety and allowing individuals to react.
Combating Pathogens
Maintaining an appropriate hot water temperature is important for controlling bacterial growth within the water heater tank. Water stored at temperatures below certain thresholds can create an environment conducive to the proliferation of specific pathogens. The bacterium Legionella, responsible for Legionnaires’ disease, can grow rapidly in water temperatures between 68°F (20°C) and 113°F (45°C). The optimal growth range for Legionella is between 77°F (25°C) and 113°F (45°C).
Legionnaires’ disease is a severe form of pneumonia that can result from inhaling water droplets containing Legionella bacteria. To prevent this, hot water storage cylinders should maintain water at 140°F (60°C) or higher. However, some experts suggest that 120°F (49°C) is generally sufficient for residential units to inhibit bacterial activity, balancing safety with pathogen control. Systems with individuals who have compromised immune systems may benefit from slightly higher temperatures, around 130-140°F (54-60°C), often combined with anti-scald devices at faucets.
Maximizing Energy Efficiency
Heating water represents a significant portion of household energy consumption, often accounting for 14% to 18% of a home’s total energy bill. Adjusting the water heater’s temperature setting directly impacts energy usage and utility costs. Every degree increase in temperature requires more energy to maintain, leading to higher bills.
Lowering the temperature from 140°F (60°C) to 120°F (49°C) can result in noticeable energy savings, potentially reducing water heating costs by 6% to 10%. This adjustment helps reduce standby heat loss from the tank and the energy needed to reheat water. For further efficiency, insulating the hot water tank and exposed hot water pipes can minimize heat loss as the water travels through the home. Considerations for energy-efficient appliances, such as dishwashers with built-in heaters, can also influence the optimal setting.
Practical Steps for Adjustment
Adjusting a hot water heater’s temperature typically involves locating the thermostat dial on the unit. For electric models, there may be two thermostats, usually found behind access panels. It is important to turn off the power to the water heater at the circuit breaker before attempting any adjustments for safety. Gas water heaters usually have a single temperature dial near the bottom.
After adjusting the dial to the desired setting, such as 120°F (49°C), it takes some time for the water in the tank to reach the new temperature. Homeowners should wait a few hours after adjustment and then use a thermometer to test the water temperature at a faucet furthest from the heater. This confirms the new setting is accurate and within a safe range. For tankless water heaters, temperature adjustment is usually done via a digital control panel.