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Added radiant heat loop to an existing hot water baseboard heat

We have a 25 year old Weil Mclain Gold GV boiler with 5 zones of baseboard heat. 2 years ago we put on an addition and added radiant heating as an additional zone to our existing boiler. It wasn't installed right and we are trying to get it to work properly. We have a contractor say we need to have a primary and secondary loops to our system with the existing 5 zones on one loop and the new radiant heat on another loop. Another contractor said we don't need it. Please advise.


  • Gordy
    Gordy Member Posts: 9,546
    edited December 2017
    Your radiant zone needs a mixing valve to reduce the water temp to the radiant zone. Tell us about the radiant installation type.

    Suspended tube.?
    Staple up with, or with out heat transfer plates?
    Sandwich over the top method?

    In all cases joist cavity insulation?

    How are zones controlled? Zone valves? Pumps?

    Primary secondary piping at the boiler is the way to go, or a hydraulic separator.
  • Ironman
    Ironman Member Posts: 7,373
    It also needs to have its own thermostat and circulator.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dave H_2
    Dave H_2 Member Posts: 553
    Adding pri/sec piping is not a bad idea but I believe it may be overkill for your project. It depends upon the size of the radiant. His concern is cold water coming back to the boiler from the radiant and therfore protecting the boiler. However, the amount of baseboard you have overshadows the size of the radiant, it will be hard to "shock" the boiler.

    Take a look at the piping arrangement and make sure it looks like the attached. Radiant will need its own mixing valve and its own circulator as well as its own thermostat.

    Dave H.

    Dave H
  • hot_rod
    hot_rod Member Posts: 22,118
    Most GV boilers have a mixing valve or device under the hood to assure boiler protection, need more details to get you some options. The type of radiant installation and the BTU load would be helpful. As well as a pic of the current piping.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Pipe it as a branch off the return with its own pump and a 3way valve. That way it gets water that’s already tempered. Can drop your return temps and get more cooler efficiency that way... if using a mod con.

    Ideally loads should be piped series parallel so DHW first, then fan coils or cast iron radiant then low temp radiant.