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Thread: Mixing Valve for Tempering water

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  1. #1
    DIY Member handyman923's Avatar
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    Default Mixing Valve for Tempering water

    I am looking to install a mixing valve on our current water heater so I can increse the temperature to 140 to 150 and not be scalded. I was looking at the Honeywell AMX300 mixing valve that attaches directly to the top of the water heater.

    The specs list the minimum flow rate as 0.25 gpm. My question is what will happen if you open a hot faucet just a trickle and have a flow rate less than 0.25 gpm? Will you get scalded with 140 or 150 deg water? Or is the mixing valve just not quite as accurate below 0.25 gpm?

    Thanks!

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    Forum Admin, Expert Plumber Terry's Avatar
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    If you're using that little water, you will have a hard time scalding anybody. The heat loss as it dribbles through the pipeing system is going to take a toll.

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    DIY Member handyman923's Avatar
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    Next question... Can a recirculating pump be added to this system? This valve has a cold water return inlet and the product manual siad this can be done if you add an aquistat and a temperature controlled pump on the return line. But then I read online that this will not work because the mixing valve does not mix unless there is flow. Therefore it would put superheated water in the hot-water lines.

    Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A recirc system draws water through the line, just like you opened the faucet, but instead of dumping it, it goes through the return line back to the WH. On a retrofit system, you may not have a dedicated return line, and then, they use the cold line and a thermostatically controlled crossover to allow flow when the hot isn't hot enough.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member handyman923's Avatar
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    So it sounds like I could use the Grundfos Comfort System with the mixing valve and not have to add a dedicated return line. Is this correct?

    Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    That should work and is reported to be a good system. FWIW, I have a RedyTemp unit (more expensive, easier, to me anyways to install) that works well.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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