Setting the temperature for your home water heater can be as easy as turning a dial. But what setting should you use? There are several factors to consider. As is so often the case, there are risk factors to be considered, and in the end you must decide what is best for yourself and your family.
One factor is safety, as hot water involves the risk of scalding. Those most at risk are small children, developmentally disabled individuals, and people with serious mobility limitations. Very hot water can cause serious harm quite quickly. Water at the top of the range of home water heaters, 140 – 150 degrees F, will cause serious burns in seconds. Water at around 120 degrees will take minutes of exposure to cause burns.
Another consideration is energy consumption, and the savings in power bills you gain by turning down the water heater. An estimation would be that you can save four percent on power use for each ten degrees you lower the water temperature. Using that estimate, lowering the water heater temperature from a high 150 degrees Fahrenheit to the EPA recommended 120 degrees F could save as much as twelve percent in energy use. That could be a considerable savings on your power bill, over time.
However, there is another important factor to consider when deciding on a setting for your water heater. That is health. The water that is safest for at-risk groups as far as direct contact with skin is not ideal for disinfection and disease organism control. Most modern dishwashers have a preheating system, so the water used to wash dishes is at 140 degrees, adequate for cleaning and sanitizing dishes. Older models, however, may lack this feature. It is important to know this when choosing your water heater setting.
Then there is Legionnaire's disease to consider. While you see the EPA recommending that water heaters be set at 120 degrees F to save energy, OSHA recommends a tank temperature of 140 degrees F. This is because at lower temperatures, your water heater can become an incubator for the Legionella bacteria, the cause of Legionnaire's disease. With the ideal growth range being 95 to 115 °F, you can see how that would be so. This may be an important consideration if your family includes those in the most at-risk groups, including older people or those with serious illnesses or impaired immune systems.
Setting the temperature for the water heater is not difficult. Gas water heaters usually have a exposed dial, easily reachable. For an electric water heater, you may have to remove a plate and pull back the insulation a bit to reach the dial. For safety, disconnect the power to an electric water heater. There may be two heating elements, an upper and a lower, so two settings may be needed. The dials for both types of water heater are calibrated only approximately, so some trial and error and testing of the water temperature at the tap will likely be needed.
To test water temperature you can use a cooking thermometer. Also available are the digital instant read models that don't even have to touch the surface, but only need to be pointed in the right direction. The temperature is usually taken at the tap closest to the water heater. A water heater set to 140 degrees F should deliver at least 122 degree water at the tap.
Clearly then, we need to choose for ourselves what is best for us. Those of us most concerned about the health risk due to bacterial infection may choose the higher setting, with water at the tap no lower than 122 degrees Fahrenheit. Those of us with family members in the groups at risk for scalding injury will want to be sure that the water heater delivers water at no more than 120 degrees F. Considering energy savings and environmental consciousness first, the lowest setting will save the most energy and the most money. Plenty of information is available related to all these factors. We should all learn what we need to know, and make an informed choice, based on the needs of our own families.