Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Max supply water temperatures for radiant.

Options
mburg
mburg Member Posts: 46
edited October 2023 in Radiant Heating

What would be the highest water supply temperature for radiant in a concrete slab, or gypcrete? 

Comments

  • Alan (California Radiant) Forbes
    Options
    On a well designed system, 130°F.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,467
    Options
    maxxon states that its gyp products resists breakdown up to 150F

    Why do you ask?  That would be a very high temperature on a floor, even with a covering over it
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mburg
    mburg Member Posts: 46
    Options
    I understand that you should never design a system that requires that high of a supply temperature, but could there be any damage to the tubing, or concrete if higher water temperatures are used? 

    Is there any concern if 180 degree water goes into a gypcrete or concrete system at startup for a bit. 
    I am replacing a condensing boiler that feeds 14 space heating zones and a 120 gallon indirect. There is currently mixing valves for all 14 space heating zones. I was considering removing all of them and allowing outdoor reset to set a supply temperature for all zones. (Except garage and basement. I will leave mixing valves on those zones) Some of the valves are leaking and it seems like a good way to get a bit more efficiency out of the system. 
    My concern is after a domestic hot water call the boilers, near boiler piping, low loss header, etc will be up to 180 degrees. Depending on how many zones are calling after a domestic call it could take several minutes or more to cool the water to a more appropriate temperature. 
    Would this be a bad idea? 
  • hot_rod
    hot_rod Member Posts: 22,467
    Options
    A small, short slug of 180F water into the radiant will not be a problem. I doubt it would last a few minutes and would dissipate quickly.
    Does your system control have a post purge setting? You could dump that higher temperature into the indirect. Most relay boxes and boilers have post purge for one circulator.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GroundUp
  • mburg
    mburg Member Posts: 46
    Options
    That’s a good idea. 
    Thanks for the input.