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Adjusting Domestic Hot Water Temperature

I have a steam heating system that also provides our domestic hot water. Having read Dan Holohan's "We Got Steam Heat" I noticed that he said "Hands in pockets, please" when discussing the Aquastat. Why? The water from our tap IS steaming hot; you can make tea from the water from the tap if you leave the hot water on a few seconds. What is a typical temperature setting for the Aquastat? My unit is currently set at about 190. Is there anything else I should know before I change the temperature setting?


  • heatboy
    heatboy Member Posts: 1,468

    you have a tankless coil for hot water, installing a mixing valve could/would/should be beneficial.


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    The Radiant Whisperer

    "The laws of physics will outweigh the laws of ecomomics every time."
  • Weezbo
    Weezbo Member Posts: 6,232
    well thats my favorite:)

    i Belive the buggs gotta DIE! i belive in hot hot water not harvey milk toast, snivler conscious, luke warm ,wannabe hot water.:) however there is a recommendation to use an anti scald ....with a steamer or someone elses boiler that is the way to travel in this world..keeps litigation down to a dull roar:) however you wont get the same colour red in the shower:))
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    The water must be 140F + to

    kill of bacteria, skin begins to scald at 110F. Put in a 'anti-scald' or 'fail safe' (automatic mixing valve [amv}).

    You may be able to lower the summer water temperature and raise the water level to 1" from the top of the glass for more efficient hot water, but in the winter it's 212F + steam and then the amv is money in the bank, FACT!
  • steve_38
    steve_38 Member Posts: 74
    it's called

    A Watts 70A mixing valve, which is designed for tempering
    demestic hot water... I install them all the time...
    anti scalding devices are usually at the faucets, why mix
    at every faucet when you can just mix it at the coil...
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    Although an

    excellent product the Watts 70A is not a device that will give the level of protection against scalding that other valves will, FACT! Also Steve, please note that by Watts' own literature the valve has a range of between 120F and 170F and therefore will allow scalding to occur as defined by the American Medical Association.

    I installed a lot of 70A's over the years (even at home) and always had phenomenal results, but time marches on. Here's the info on their new valves BTW;
  • Dave Yates (PAH)
    Dave Yates (PAH) Member Posts: 2,162
    Partial cures

    To really address the hot water issue, you need to treat the entire system, which consists of three parts: point of source; distribution network; and points of use.

    At the point of source, you'll need to maintain an internal temperature above 140 F and, in the case of a domestic coil, much higher to hit the flow rates they're rated for on a constant draw. In order to lower the distribution temperature, you'll need an ASSE 1017 thermostatic mixing valve & that should be set to deliver a minimum of 133 F. A heat trap is essential to protect the valve. The 133+F will help to suppress any bug populations. Constant circulation would be nice, but not practical with a domestic coil. The human threshold for pain is 106 F & 120 is not a safe bather temperature for hot water delivery. 3rd degree burns can occur with just a few minutes contact time at 120F (elderly and infants are most susceptable). Each point of use where human contact occurs should be examined for a scald guard ASSE 1016 certified device & there are three basic types: P-only, which react to changes in pressure - but are blind to temperature changes; T-only, which react only to temperature fluctuations; and P/T, which combine both features for a higher level of protection.

    110 F systems offer highly suitable amplification for bugs, which is why the final reduction in delivery temperature should be as close as possible to the outlet of the points of use.

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