radiant heat - low circulation problem

Discussion in 'Home Repair' started by elai, Dec 6, 2006.

  1. elai

    elai Guest

    Hi - I'm building a new house in the Boston area and installed a
    Warmboard radiant system with Viessmann wall hung condensing boiler.
    I'm having problems getting this system working correctly. It appears
    as if I'm not getting enough circulation. The Grundfos UP26-64 pump
    seems to be powering up and running (I even took the cover off and
    confirmed it was spinning and there are no noticible dings or scratches
    in the plastic impellers). I was able to fill the system fine, but I
    appears as if I'm only getting around 2-3 GPM total for the entire
    system at the manifold, even when I turn off all manifolds except for a
    small one with only 4 loops. The Viessman is outputting 25 psi.

    When I run the boiler at a 90-95 degrees, it doesn't even come close to
    heating up any of the tubing. After cranking it up to 150 degrees, the
    house is now warm, but I'm pumping (and wasting) a lot of heat.

    Seems like a circulation issue? Anyone have any ideas? Bad pump?
    elai, Dec 6, 2006
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  2. elai

    elai Guest

    After 2 hours of playing around and swapping pumps, I figured this out
    last night. My plumber had put a mixing valve in between the low loss
    header and the radiant controls. I guess this isn't usually a problem,
    but for some strange reason my mixing valve isn't working right...
    when I shut it off, I now get full flow at all my 6 manifolds. With it
    on, I get almost no flow. Weirdest thing - plumber and my radiant
    designers can't figure it out, but the valve is coming out ASAP.

    Tom - not sure about your system, my radiant designers did all the heat
    loss calculations for my house and tell me I'm supossed to be able to
    run this system at 90-95 degrees. Obviously, if I'm not getting enough
    flow to the manifolds, the water isn't moving fast enough thru the
    system, and the system doesn't heat up as quickly (if at all)...
    especially where I'm doing a cold start when it's 20 degrees outside.
    It was losing most/all of it heat just running between the boiler and
    the manifolds. Thus, my boiler was working overtime heating up water
    to 90 degrees plus and we weren't getting this heat into my system - so
    it was "wasted". To compensate, I had to crank the boiler up to
    140-150 degrees, just so we could get some heat into the system. They
    also tell me that under stable conditions, the drop from your supply
    temp and return temp should be 15-20 degrees.... I was getting
    something like 70 degrees drop and still not getting the house warm.

    Now with proper flow, I should be able to run it at 95 degrees and
    still heat my whole house (saving a lot of energy vs heating to 140).
    Plus these boilers are [supposedly] designed to run these systems - it
    has different settings depending on what kind of heating system you're
    using - radiant, baseboard, etc.

    I just cranked the boiler back down, but they tell me I should be able
    to run the boiler at around 100 degrees, my supply lines should be
    around 90 degrees and the return lines should be around 70-75 degrees.
    We'll see. This is my first time with radiant, I've spent a lot of
    money on it, i'm just hoping it works...

    Anyone else have problems with these mixing valves?
    elai, Dec 7, 2006
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  3. elai

    pi Guest

    pi, Dec 8, 2006
  4. elai

    pi Guest

    pi, Dec 8, 2006
  5. elai

    pi Guest

    pi, Dec 8, 2006
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