Hot Water Mixing Valve
Buying & Installation Tips

Thermostatic mixing valve for water heaters

Why installing a hot water mixing valve is a good idea. Also known as a tempering valve, anti scald valve and shower mixing valve, it is designed to lower the hot water temperature and avoid burns.

Hot water mixing valves are used in residential water heating when taking a shower, bath or hand-washing, to reduce the temperature at the point-of-use, by mixing the hot and cold water in the branch water line. Check out the buying and installation tips.


Mixing valves are also known as anti-scald mixing valves, tempering valves or shower mixing valves and are recommended for every household, especially if there are kids and seniors.

In order to adjust and control the temperature, every water heater utilizes the thermostats. The instructions on of how to use it, about the safe and scalding temperatures, you can find in almost every user manual.

The safe and unsafe temperatures in water heaters

  • The recommended and also factory set temperature setting is 120 F.
  • If the temperature is 120 F, it will take 5 min for 2nd and 3rd-degree burns on the adult skin.
  • For the temperature of 130 F, it will take 30 sec.
  • For the temperature of 140 F, it will take 5 sec.
  • For the temperature of 150 F, it will take 1.5 sec.
  • For the temperature of 160 F, it will take 0.5 sec.

Note; water heaters with the hot water temperature between 68 and 122 F could lead to development of the Legionella bacteria.

As you can see from the above facts hot water is a great risk to one’s health. By installing the hot water mixing valves this problem can be eliminated. The valve restricts the scalding hot water delivery at the tap while maintaining the safe temperature and environment for the whole household.

Based on the recommendations, the heaters should be set around 130 F which provides hot water with the temperature hot enough for dishwashing while preventing the development of harmful bacteria.

Advantages of the mixing valves

Great advantages of the mixing valves for hot water are the ability to extend the capacity of tank storage type and tankless heaters and of course significantly reduce the risk of scald injuries in your home.

As the mixing valve provides protection and comfort for your family, it also prevents the bacteria growth. With the thermostatic mixing valves, it is easy to avoid low temperatures where bacteria is active, you can set the temperature high enough to prevent scalding and to eliminate bacteria.

One of the common applications are in solar heater when heated fluid inside the solar panel is too hot to be safe, so the tempering valves are used to lower the temperature.

Types of the hot water mixing valves

There are different types of mixing valves, which can meet various installation requirements. The most popular sizes of these tempering or anti-scalding valves are 1/2" and 3/4" which are usually the most common fitting sizes. Hot water mixing valve can be found as hydraulically or thermostatically operated and as the 3-way and 4-way motorized valves.

Hydraulically and thermostatic mixing valves

Hydraulically operated tempering valve, or pressure balanced type, has the stainless steel spring loaded in the water supply to allow cold to mix with hot water. Mixing valve bodies are usually made of brass to resist the corrosion.

These types of mixing valves do not automatically control the outlet temperatures, but they require manual adjustment.

Thermostatic mixing valves, TMV, is used to control the temperature by mixing the cold and hot water to the temperature that was pre-selected by the user.

The valves are using the thermally sensitive mechanism inside the valve that allows proper mixing of hot and cold water. TMV mixing valves offer precise control of the temperature and pressure, no matter how the inlet temperatures or pressures vary over time.

3-way motorized mixing valves

3-way motorized mixing valves have three ports, one for hot, one for cold water and one for mixed water, which is the result of the desired, pre-set temperature. Basic manual mixing valve has the flow element or spool inside the valve, adjusted with the knob, so it mixes the cold and hot water in the accurate proportion of the desired temperature.

The more advanced 3-way mixing valve is the one with the automatic temperature control that adjusts itself to compensate for changes in the water entering. Motorized actuators with the electronic temperature controller are used for self-adjusting valves.

4-way hot water mixing valves

4-way mixing valves have four ports. One portion of the entering cold water is mixed with the portion of hot, to create the desired temperature. To boost the temperature of the heater, the remainder of the hot water from above steps is blended with the remainder of the cold.

Keep in mind that mixing valves are factory set to lower temperatures, with the range from 80 F to 120 F, so you might not have the temperature high enough for dishwashing. This is one of the common complaints from the user reviews.

If you are not sure about the outlet water temperature at the tap, you can check it by running the hot water through the tempering valve (open the tap) and measuring the temperature with the thermostat. It should be the same as the set point on the valve.

Popular brands

  • Honeywell
  • Watts
  • Leonard
  • Taco
  • Danze
  • Danfoss
  • Heimeier
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