Hot Water Mixing Valve

Hot water mixing valves are used in residential water heating; for showering, bathing or hand-washing, to reduce the point of use temperature by mixing hot and cold water in the branch water line.

Mixing valves are also known as anti scald mixing valves, tempering valves or shower mixing valves.

Water heaters are using thermostats to adjust and control the temperature. Within the first pages of almost every heater manual, you can read about the safe and scalding temperatures. This guideline about buying hot water mixing valve or simply tempering valve will make the decision easier, especially if you have kids.

Recommended hot water temperatures and why using anti scald mixing valve

  • The recommended and 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 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.

By installing the tempering valve or anti-scalding valve you will restrict scalding hot water and maintain safe temperature. Heaters are usually set to, based on my experience and other user reviews, around 130 F to provide decent temperature for dishwashing and to prevent the development of harmful bacteria.

Advantages

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


Hot Water Mixing Valves Types

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 size. Hot water mixing valve can be found as hydraulically or thermostatically operated, and as 3-way and 4-way motorized valves.

Hydraulically and Thermostatic mixing valves

hot water mixing valveHydraulically 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, they require manual adjustment.

thermostatic tempering valve for water heatingThermostatic 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.

Thermostatic hot water mixing 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 exiting temperatures and pressures, 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, to mix the cold and hot water in the accurate proportion for desired temperature.

More advanced 3-way hot water mixing valve is the one with the automatic temperature control that adjust 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 hot water mixing valves have four ports. One portion of the entering cold water is mixed with the portion of the hot to create desired temperature. To boost the temperature to 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 on 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 I have read in the user reviews.

If you are not sure about the outlet water temperature and 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 hot water mixing valves brands are coming from Honeywell, Watts, Leonard, Taco, Danze, Danfoss, Heimeier and many other.

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