Excessively hot water temperatures can result in scalding. People generally take showers at 41 °C to 49°C (105°F-120°F), often by blending hot water at 60°C (140°F) with cold water with a mixing valve in the shower. Most people experience temperatures above 43°C (110°F) as uncomfortably hot.
Some commercial uses require higher temperatures. The minimum for a sanitizing rinse for a commercial dishwasher or laundry is 82°C (180°F). Generalpurpose cleaning and food preparation requires 60°C (140°F) water. Temperatures above 60°C can cause serious burns, and promote scaling if the water is hard. However, high temperatures limit the growth of the harmful bacterium Legionella pneumophila, which causes Legionnaire's disease. Water heaters for high temperature uses have larger heating units, but the tanks can be smaller because less cold water has to be mixed in. Some appliances, such as dishwashers, heat water at the point of use. Codes may regulate or limit high water temperatures.
Lower temperatures are less likely to cause burns, but may be inadequate for sanitation. Lower temperature water loses less heat in storage and in pipes, saving energy. Smaller heating units are adequate, but larger storage tanks are needed. Solar or waste heat recovery sources work better with lower temperature water heaters. For energy conservation, use the lowest possible temperatures.
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