The temperature of bradford white water heaters phoenixWater Heaters is pre-set.

Most homeowners know that residential water heaters are pre-set at the factory to a maximum temperature of 120 degrees to prevent scalding, which can occur very quickly at temperatures above that level.   Unless other safety measures are in place(1), serious scalding from excessively hot water can occur in a matter of just seconds, especially where children and the elderly are concerned.

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(602) 273-7473

The factory set temperature of Water Heaters won’t kill bacteria.

What’s not as commonly known is that this temperature setting (120 degrees F) is lower than the temperature required to kill bacteria.  Depending on the demand made on your hot water heater, some of the water (in particular the water at the bottom of the tank) may stagnate and become a fertile breeding ground for all kinds of bacteria, including the Legionella bacteria that can cause Legionnaire’s Disease.  Legionella bacteria are commonly found in potable water supplies and they can multiply in warm (not hot) water systems to a level that poses a potential health hazard.(2)

To kill the Legionella bacteria, water temperatures need to be above 135-140 degrees. But, as mentioned in the previous paragraph, that is not considered a safe setting for residential hot water heaters as water temperatures that high can cause severe scalding.

Water Heaters and Hot Water Systems need to balances risks.

Seem like an impossible conflict?  Maybe not.  The same white paper referenced above (2) makes the following suggestions for solutions to the conflict:

Install a Temperature Actuated Mixing Valve. Installed at or near the outlet of water heaters, temperature actuated mixing valves adjust the temperature of the water as it leaves the heater and before it reaches the point of use. (NOTE: The American Society of Safety Engineers recommends, however, that where water heaters are set at temperatures above 120 degrees and where residents are relying on a temperature actuated mixing valve as a safety feature, the hot water system should be supplemented with additional point of use safety devices.(3) )

Install a Mixing Valve at the shower or tub. Available on shower and tub/shower valves, the mixing valve automatically mixes hot and cold water at the point of use, to provide and maintain a blended water temperature within a specified, safe temperature range. Normally, in residential use these are point-of-use devices that work to ensure a constant, safe shower and/or bath water temperature, and prevent scalding.

Install a Temperature Limiting Device (or multiple Devices) like the American Standard(4) line of fixtures that include an Adjustable Hot Limit Safety Stop. In plumbing fixtures installed at lavs, kitchen sinks, bathtubs, etc., the hot limit safety stop prevents the water temperature from exceeding a preset, safe level. Available on single handle fixtures, the device works by restricting the rotation of the handle to limit the amount of hot water mixed with the cold water, thus effectively lowering the maximum water temperature and helping to reduce the risk of hot water scalding. Until recently available only on luxury plumbing fixtures, this option is now widely available at a price point that makes it generally very affordable for every home.

Questions about Water Heaters or Water Heater Safety?  Give us a call!  An experienced plumber is always available during business  hours to answer your questions.

Stevens Plumbing Heating & Air Conditioning
(602) 273-7473

(1) The installation of these plumbing safety devices, when done properly, can allow the temperature of hot water heaters to be increased to a level that will restrict bacterial build-up while still preventing scalding.

CAUTION: DO NOT INCREASE THE TEMPERATURE OF YOUR WATER HEATER until, and unless, you have had the necessary hot water safety devices correctly installed by a plumbing professional.


(3) ASSE Standard #1071-2012 ASSE Board Approved: August, 2012 ANSI Approved: October, 2012