Installing a Tempering Valve

A Tempering Valve, Mixing Valve, Thermostatic Mixing Valve (TMV) or Anti Scald Valves is a valve that blends hot water (stored at temperatures high enough to kill bacteria) with cold water to ensure constant, safe outlet temperatures, preventing scalding.
Reliance IS102 Tempering Valve: HeatGuard accuracy of out let temperature is 3°CReliance IS102 Tempering Valve: HeatGuard accuracy of out let temperature is 3°CTempering Valve Cutaway: Cut-away showing the innerds of the Reliance IS102 tempering valve.Tempering Valve Cutaway: Cut-away showing the innerds of the Reliance IS102 tempering valve.


We installed one with our solar hot water system because of the scalding hot water the system produces on a sunny day. Now when someone opens the hot water to wash their hands instead of 160°F water they will get 120°F. Since this problem is resolved we can go ahead and store the hotter water without fear of burning someone or a customer's hands and the tank's hot water will last longer.

Basically we put in-series this valve assembly in the hot water line exiting the hot water tank . Also teed into the valve is a supply of cold water. If the water from the hot tank is above the requested temperature then the bi-metal spring will partially open up the valve and allow cold water to mix with the hot bring down the exiting water temperature.
Tempering Valve Location: Location ready for the tempering valveTempering Valve Location: Location ready for the tempering valveTempering Valve in Place: Tempering Valve inplace and the input hot water line connectedTempering Valve in Place: Tempering Valve inplace and the input hot water line connectedTempering Valve Installed: Solar hot water Tempering Valve installed with the input hot, input cold and output warm lines connectedTempering Valve Installed: Solar hot water Tempering Valve installed with the input hot, input cold and output warm lines connected


Automatic vs. Manual Mixing Valves Work Differently

An automatic mixing valve includes a temperature sensing mechanism that automatically adjusts the amount of cold mixed in with outgoing hot water to maintain the desired output water temperature.

A manual mixing valve such as those often installed at older tankless coil hot water systems uses a simple gate valve that is manually adjusted by the homeowner. At a minimum the homeowner may have to adjust this valve seasonally depending on whether or not the building is also being heated by the same boiler as during the heating season the boiler will be kept hotter than during the rest of the year, making the outgoing hot water too hot.