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Water Temp

dennya Member Posts: 13
could someone tell me why the engineers do not want water temp's above 120 degrees F when using in-floor heat in a concrete floor


  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    Do you want your floor above 120 degrees? Bit of a safety hazard there, I'd say.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,248
    Hello, Done wrong, it could make for some really uncomfortable floors. What are you trying to do? Perhaps you could share your design so folks here could tell you what they see in it, both good and not so good? ;)

    Yours, Larry
  • Leonard
    Leonard Member Posts: 903
    I can't stay on roof on a hot summer day....... hot foot.
    EBEBRATT-Ed Member Posts: 15,345
    It would be very uncomfortable and damage the floors
  • hot_rod
    hot_rod Member Posts: 21,878
    Now some times you might need to send supply temperature to slabs at high temperatures, carpet and pad over a slab for example.

    But surface temperature below 85F
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • dennya
    dennya Member Posts: 13
    My biggest side to this question was whether or not higher than 120 degrees would damage the concrete. I have three sons who have built new homes recently and we've installed in-floor heating in the basement/garage floors. Each time I did put mixing valves in to these zones but curious the necessity. I don't think that running @ higher temps would actually make the concrete too warm to walk on by the time the zone was satisfied, or if the concrete temp would ever reach water temp. And being an old service tech, I hate putting mechanical devices in water which is sure to fail (in my opinion)
  • Dave H_2
    Dave H_2 Member Posts: 547
    There are two reasons the water temp needs to be tempered.

    The first is concrete with excessive water temps can degrade over time. I can't remember the actual number at the moment, but if its straight boiler water, definitely no good.

    The second reason is for control of the system, if you send too hot of a water temp to any radiant floor, you will get large air temperature swings, in excess of 5 degrees most times.
    Which means if you set the stat to 70 and the floor call for heat and you start throwing a real high temp to the floor, when the thermostat satisfies, the floor will still have a ton of energy in it which will continue to radiate into the room, and 75 can be easily achieved.
    Now the reverse starts to happen, as the room starts to cool down from 75, the radiant has been off for a long period of time and by the time the stat call again, we need to charge the floor again, by this time the floor is cold and before any energy goes into the room, the air temp can reach 65 before it starts its upward climb.

    Dave H.
    Dave H
  • Brewbeer
    Brewbeer Member Posts: 616
    All mechanical devices have a certain useful service life. When that service life is over, it gets replaced. Whether its a boiler, mixing valve, or a car, no mechanical device lasts for ever.

    You could use a modulating condensing boiler that sends water to the floors at the correct temp needed without having a mixing valve, but a modulating condensing boiler is also a mechanical device.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    There is an engineering reason, besides the safety ones. The higher temperature will lead to high temperature gradients across and through the concrete. This will crack the concrete. Less if you use fiber reinforced concrete, but with regular concrete you will -- guaranteed -- get cracking. This will allow moisture to get to your rebar, which will corrode the rebar, which will crack the concrete further.

    Since there is no need to do it, don't do it. Run the system correctly -- the water temperature has no need to be more than about 10 degrees over the target slab temperature at any time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England