What are they, why do I need one and how much are they?
What is the purpose of a tempering valve? A tempering valve takes the hot water from a water heater (usually around 60-65 Celsius) and the cold water supply and mixes them to create a tempered hot water supply limited to 50 Celsius. The aim is to reduce the number of incidents of scalding of children and the elderly.
To give you an rough idea, at 50C it takes 7 minutes to cause a 2nd degree burn and 9 minutes to cause a 3rd degree burn. By comparison, at 60C it takes just 3 seconds to cause a 2nd degree burn and 5 seconds to cause a 3rd degree burn.
50 Degrees Celsius doesn’t sound like much but 40C is considered a very hot shower. Washing dishes with 50C water would be fairly uncomfortable without gloves. You might ask why they don’t just reduce the temperature of water in tank and not store it at an unnecessarily high temperature. The answer is simple and it is because water kept in a tank between 25 and 50 degrees centigrade creates the perfect breeding ground for the bacteria that causes Legionnaires’ Disease. That is why it is generally kept at a minimum of 60C.
Why must one be installed
A change to the plumbing code was made in 2013 requiring that all hot water heaters be fitted with a tempering valve when supplying sanitary fixtures. What this means is if you have a heater installed that supplies water to a sanitary fixture (anything other than a kitchen sink or laundry tub) it must be fitted with a tempering valve. If your home was built in the last 8-10 years or so you probably already have one. If you already have one you can continue to use it with the new heater or opt to replace it as they tend wear as with anything else.
How much are they
Fitting a tempering valve isn’t terribly complicated however it does require changes to the pipework to accommodate it and generally costs around $150 inc GST supply and fit at the time of heater installation or $225 inc GST if retrofitted to an existing heater. If the old heater had an existing tempering valve and you just wish to replace it along with the heater it is a fairly simple task with little or no modification necessary to the existing pipework therefore the cost is only for the valve itself which is $75 inc GST