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Caleffi Domestic Hot Water mixing valve question for Hot Rod

bob eck
bob eck Member Posts: 930
Question for Hot Rod
When installing a Lochinvar Noble combi boiler with their brazed plate heat exchanger and using a Caleffi Domestic Hot Water mixing valve say the mix is set for 120F to the faucets what is the temp coming out of the brazed plate heat exchanger need to be before the mixing valve does its mixing with the cold water coming in.
I was told in a training class today that the hot water going into the Caleffi mixing valve has to be 27F higher than the temp going out to the faucets.
120F going to faucets hot water in from domestic side of the combi boiler needs to be 147F before the mixing.
Is this true?


  • hot_rod
    hot_rod Member Posts: 22,263
    Correct, to be accurate the valve needs some differential. the valve will work with tighter numbers but it will hunt around. With a small differential the small pin activated by the wax motor will be at the end of its stroke and not regulate accurately. This is true of all thermostatic valves, they need that differential.
    Try it at different temperatures see how it regulates for you. You could also lower the mixed temperature a bit.

    It’s possible the Nobel can regulate the output accurately without the mixer.

    ASSE is developing a few new standards 1083, 1084 & 185 I think, tankless and combos could meet the standard 1017 & 1070. They can regulate output closely, eliminating the mixer requirements.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bob eck
    bob eck Member Posts: 930
    Hot Rod thanks for the info.
    How does a Honeywell AM100-US-1LF mixing valve work on a 3 degree F difference.
  • mattmia2
    mattmia2 Member Posts: 9,749
    Is the large differential needed for the total shutoff requirement? Will it regulate accurately at lower differentials but more than 3 degrees?
  • DZoro
    DZoro Member Posts: 1,048
    Interesting, I actually have my personal Noble plumbed direct to my master, and through mix valve the rest of the home. I'd have to say after over 2 years with this set up. The mix valve side of the home has more variances than direct out of the Noble. I'm using the Honeywell. Noble is set @140.