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Adding radiant zone

I’m adding a radiant zone to my Weil Mclain ultra 155 boiler. I have two high temp radiator zones already. The manual says that if the radiant zone is less then 30% loss then I do not need a mixing valve. What will happen when a high temp radiator calls at the same time?


  • DZoro
    DZoro Member Posts: 1,048
    Your going to get the high temperature. What type of radiant are you adding? How large? A big picture of your current system will help tremendously.
  • williamgxxx
    williamgxxx Member Posts: 4
    Thank you for your help.
    I have primary/secordary piping with two circulators for radiators and a indirect fired water heater I’m thinking of adding a 300’ loop in 1/2” pex for a subfloor install under a kitchen.
    Why would Mclain suggest this?
    EBEBRATT-Ed Member Posts: 12,016
    You need some type of mixing valve. If not the radiant which must be supplied with less than 120 degree water will get high temperature water
  • DZoro
    DZoro Member Posts: 1,048
    That means that particular zone should be less than 30% of your system design btu's. Not 30* lower water temperature. For radiant floor load in your case like Ed said will need some type of mixing device to lower the water temperature in that zone. Note: this device placement should be after all of your high temp. zones.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    edited January 2018
    Or, hang finned tube element in the joist bays. Ultra-Fin.com

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.