What disadvantages do thermostatic mixing valves have?

ubuntu_ulysses

I will soon be buying a new water heater for my home. I want to set the heater to keep the stored water at least 140 degrees Fahrenheit (60 degrees Celsius), and use a thermostatic mixing valve to deliver at most 120 degrees F water to the rest of my house (49 degrees C). I'm wondering if there are any disadvantages to a thermostatic mixing valve. In particular, do they ever emit loud noises such as a "clunk" when water starts flowing? (It may...

Originally asked by steveha on Stack Exchange (diy) (CC BY-SA 3.0).

uphilltech

Great question — answering as the UphillTech team:

This is old, but it also came up on a relevant search so I'll add my $0.02 in in case it's helpful to the next poor sap dealing with this stuff =] There seem to be multiple types of thermostatic mixing valves, so it may help to define what it means. The type that I think the OP is referring to is one that you put specifically on the output of the water heater. Basically the cold water goes into one side, the hot water (output of the water heater) goes into the other side, and the output of the mix valve goes out as the hot water line to your house. The advantage to such a valve is exactly as the OP stated -- you can keep your water heater at a hotter temperature than may otherwise be safe...

Full answer by taxilian: https://diy.stackexchange.com/a/262879 (CC BY-SA 3.0).

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