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Tempering valve for DHW with bypass

Just looking for some advice . I had a oil fired water heater replaced with an indirect this year. The oil fired Bock water heater ran 18 years before leaking and was set to 125 degrees on the aquastat. You couldn’t run that system out of hot water. The water was clean and never gave me the odor I get now. The installer set the indirect to 120 degrees. I really like the fact at the lower temps, I get a warm water at the sinks etc without having to mix with cold. . With the indirect I get some odors on initial draw that lead me that we have a bacteria/sulfide problem. I am on city water and given the last water survived 18 years before leaking I don’t think water quality is the issue. Perhaps the heating surfaces of the oil fired water heater was hot enough to kill the bacteria. I bumped the indirect

up to 125. It helped but I think I need to run this hotter. So I am looking at having a tempering valve installed. But I do like hot water in the kitchen. I like to cook and want to make sure the dishwasher and the kitchen have hot enough water to clean cutting boards etc, I am thinking a bypass around the tempering valve for the kitchen and perhaps the washing machine. No kids in the house . Good idea or not?


  • Leon82Leon82 Posts: 589Member
    Dishwashers heat their own water so you don't need to worry about that.

    Storing water that low can cause bacteria to grow.

    You could run a separate line to the kitchen but I don't know if that meets code. Depending which code you are on there probably should have been one installed.
  • hot_rodhot_rod Posts: 11,259Member
    I agree with Leon, dishwashers can heat the water and also a heated dry cycle will provide elevated temperature on the dishes.

    Most soaps work fine with 120F, even cold water detergents, down to 60° work well now. 80- 90° is a typical warm wash temperature.

    I suppose if you are washing diapers, temperatures above 130° may add some piece of mind :)

    Whites wash better with hot, but hot can also shrink, fade and damage some fabrics from what I read.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • jimctjimct Posts: 9Member
    Hence the reason for the tempering valve
    To be able to store the water at 130 degrees
  • HVACNUTHVACNUT Posts: 2,036Member
    > @jimct said:
    > Hence the reason for the tempering valve
    > To be able to store the water at 130 degrees

    You would set the indirect aquastat from 140 to 160, then use the thermostatic mixing valve to temper the domestic hot down to 120. Also install a 3/4 sweat x 1/2 female x 3/4 sweat tee for an insertion thermometer. The thermometer should have a 1/2" dry well to insert the thermometer.
    I've seen high temp used commercially for laundry but I don't recommend it for domestic. It doesn't take much to get a 2nd or 3rd degree burn above 120.
  • hot_rodhot_rod Posts: 11,259Member
    120-122° is the common setting for mixing valves on residential systems. So the tank temperature, ideally, is 25° hotter that the mix for the 3 way valve to be able to regulate accurately. I'd suggest 145- 150° max.

    Keep in mind the higher the tank operating temperature the shorter the life expectancy, more mineral precipitation at higher temperature. Also more metal fatigue for cold incoming water and high operating temperature in the tank.

    It would be good to know how the city is treating the water. Sme of the treatments like chloramines and polyphosphates can give you different odors.

    Check the chloride levels also, if it is a stainless tank, they have a very tight requirement, or warranty is void.

    A quality brand glass lined steel indirect tank, operating at 140 should last a good long time. As your previous tank did.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • bob eckbob eck Posts: 849Member
    Store water at 140 F or so. Use a good mixing valve for domestic hot water. Coming off the indirect water heater you could put a tee in that line to take off a hot 140 F supply (must be careful not to go to a faucet where you can burn someone. Does local code allow this?) line to run where you need it. Then put the mixing valve in that line.
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