1:5:10:365 EcoTip Blog

May 25, 2008

:146 Reduce Temperatures

1:5:10:146 EcoTip: Today’s tip is to reduce hot water heater temperatures to save energy, but it has a caveat. Reduced temperatures in hot water heaters have proven to be a source of the infectious bacterium Legionella pneumophila. It is currently estimated that Legionnaire’s disease affects between 10,000 and 100,000 people each year. So how does one achieve energy savings and safety from this disease at the same time? In the additional reading below I have provided both the Department of Energy and OSHA’s perspectives. I then tell you how our family manages to balance the risks and the benefits.


 Additional Information:

The Department of Energy says:

You can reduce your water heating costs by simply lowering the thermostat setting on your water heater. For each 10ºF reduction in water temperature, you can save between 3%–5% in energy costs.

Although some manufacturers set water heater thermostats at 140ºF, most households usually only require them set at 120ºF. Water heated at 140ºF also poses a safety hazard—scalding. However, if you have a dishwasher without a booster heater, it may require a water temperature within a range of 130ºF to 140ºF for optimum cleaning.

Reducing your water temperature to 120ºF also slows mineral buildup and corrosion in your water heater and pipes. This helps your water heater last longer and operate at its maximum efficiency.

Consult your water heater owner’s manual for instructions on how to operate the thermostat. You can find a thermostat dial for a gas storage water heater near the bottom of the tank on the gas valve. Electric water heaters, on the other hand, may have thermostats positioned behind screw-on plates or panels. As a safety precaution, shut off the electricity to the water heater before removing/opening the panels. Keep in mind that an electric water heater may have two thermostats—one each for the upper and lower heating elements.

Mark the beginning temperature and the adjusted temperature on the thermostat dial for future reference. After turning it down, check the water temperature with a thermometer at the tap farthest from the water heater. Thermostat dials are often inaccurate. Several adjustments may be necessary before you get the right temperature.

If you plan to be away from home for at least 3 days, turn the thermostat down to the lowest setting or completely turn off the water heater. To turn off an electric water heater, switch off the circuit breaker to it. For a gas water heater, make sure you know how to safely relight the pilot light before turning it off.


OSHA says:

  • Maintain domestic water heaters at 60°C (140°F). The temperature of the water should be 50°C (122°F) or higher at the faucet.
  • Avoid conditions that allow water to stagnate. Large water-storage tanks exposed to sunlight can produce warm conditions favorable to high levels of LDB. Frequent flushing of unused water lines will help alleviate stagnation.
  • However, if you have people living with you who are at high risk of contracting the disease, then operating the water heater at a minimum temperature of 60°C (140°F) is probably a good idea…. [but not] If you have small children or infirm elderly persons who could be at serious risk of being scalded by the hot water. Consider installing a scald-prevention device. http://www.osha.gov/dts/osta/otm/legionnaires/faq.html
  • The way I deal with these conflicting issues is by:

    keeping our water heater at a lower temperature setting that delivers approximately 110 degree water at the faucets, so the water won’t scald and we save energy.

    Not allowing water to stagnate in the hot water heater or pipes. We do this by using every hot water fixture on a rotating basis (at least every third day). Also our hot water heater is small enough so that we run out of hot water after two ten minute showers. This is a good sign that the hot water heater has been flushed which will help prevent Legionella from building up.

    If were going to be away for more than three days, then the hot water heater is turned off. It is a gas unit with automatic ignition so lighting the pilot is not a problem. Below temperatures of 68 degrees, Legionella goes dormant and doesn’t grow.

    Keeping scale and sediment from building up in the hot water heater. The debris can act as a breeding ground for bacteria and provide temperatures that promote the growth.

    This is one of those issues where there can be no hard and fast rules, but hopefully the above information will help you design a strategy that will work for your family.

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