Above most hot water tanks today there is a device known as a Thermostatic Mixing Valve also called a hot water tempering device. Water from the hot water tank enters the valve on one end and cold water enters the other end. The valve then mixes the two together so that the water coming out of the taps is hot but not scalding.
Most people prefer their hot water around the 40°C temperature range. Unfortunately, that is also the ideal temperature for bacteria such as Legionella to grown in the tank. Legionella was found in stagnant water tanks that led to 34 deaths in the United States in the late 1970’s. Fortunately, this bacteria does not survive in water above 60°C.
By using a mixing valve we can keep the water in the tank hot enough that bacteria will not grow while keeping the water coming out of our taps safe against burns.
To avoid potential harm, have the temperature of your tank set to about 60°C and then adjust the mixing valve so that the water coming out of your taps is hot but not scalding.
Most modern washing machines (dish and clothes) have built-in heaters to heat up the water for better cleaning to compensate for tempered hot water.
A side benefit of the mixing valve is that it artificially increases the size of the tank. So, a smaller hot water tank (with a mixing valve) can provide more or less the same volume of hot water as a larger tank without the mixing valve.
Have you noticed that hot water at the tap seems to be warmer in the summer and cooler in the winter? That’s because the temperature of the cold water varies with the temperature outside while the hot water in the tank stays the same.
Temperature Time to Cause
of Water a Bad Burn
66°C (150°F) 2 seconds
60°C (140°F) 6 seconds
52°C (125°F) 2 minutes
49°C (120°F) 10 minutes
Steven Silva is a Sales Representative with Royal LePage Your Community Realty
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