Tempering Valve

[Jerry Simon]

Why would someone install a tempering valve on the hot water heater pipes?  Wouldn't one just keep the heater's thermostat set at 120-125 degrees?

Edited October 25, 2019 by Jerry Simon

[Jim Katen]

It allows you to crank up the temperature of the water heater, giving you, in effect, a greater volume of 120-degree water than you would otherwise be able to store. 

Kind of like those cans of orange juice concentrate. 

[inspector57]

It also allows the heater to be raised to a temperature sufficient to control Legionella bacteria 140 + but allow delivery of a lower temperature to point of use.

I have seen one such heater equipped from the factory with the valve setup that was rated to replace two 50 gallon heaters with one 50 gallon unit. Seemed to work perfectly and was in grand scheme cheaper to operate.

[Marc]

A downside is reduced efficiency since more heat is going up the stack.

[ejager]

The CDC and other sources recommend tempering the water at the point of use. Here, the tempering valves are typically located in the master bathroom and protect the bathrooms only, with no tempered water at the kitchen.

Quote

Make Sure Water Temperatures Are Right

Legionella grows best within a certain temperature range (77°F-108°F). To keep water outside the range for Legionella growth, it is important to keep cold water cold and keep hot water hot.

• A note about cold water: In warm climates, water in pipes that carry cold water may reach a temperature that allows Legionella to grow.
• A note about hot water: It is important to maintain water heaters at appropriate temperatures while following local and state anti-scald regulations. Sometimes maximum temperatures allowed by your state may be too low to limit Legionella growth. Engineering controls that mix hot and cold water together at or near the point of use can reduce the risk of scalding while allowing water in pipes to remain hot enough to limit Legionella growth.

https://www.cdc.gov/legionella/wmp/overview/growth-and-spread.html

There are always compromises in a home. I think a little money for safety is a good thing.

[Plumbing and Electrical]

It can adjust your water temperature