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School me on radiant zone control

Jon_E Member Posts: 12
I am trying to learn what I can about zone control, in anticipation of adding new zones to a radiant heating system that had some design 'issues' from the very beginning. I have five zones on my system - four radiant heating zones and one for domestic hot water. One zone goes into a 6-port Caleffi manifold for my basement floor. Another zone goes into a 'plumber-made' two-port manifold for heating two bathrooms on my second floor. The remaining two zones are intended for staple-up tubing on my main floor, which have never been completed or hooked up. I have run out of room on my Wall for any additional manifolds or piping of any kind, and will actually have to install something on the ceiling or on an adjacent wall if I want to use the remaining two zones and if I don't re-plumb the system.

I am trying to figure out if "shrinking" the main heat loop and reducing the number of hard-piped zones, will work in conjunction with a single new manifold and thermal actuators to control the temperature of each circuit (loop?), and thereby give me some room to lay everything out in one place, or I should just completely separate out each zone with its' own circulator pump, mixing valve and manifold? I would leave the basement zone alone, it's working fine. I'd also leave the hot water alone, that's irrelevant. But, can I combine all of the remaining circuits/loops of PEX onto a single manifold? There's a total of five circuits installed (two active, for the upstairs bathrooms) and two more that still need to be stapled up and insulated. That would require a seven-loop manifold and would, in my mind, allow me to use a single circulator pump, a single mixing valve, and a bunch of thermal actuators on the return side of the manifold that would control the loop temp for each loop. It will also significantly reduce the space this system takes up on my basement wall.

Not sure what to do, I have literally been kicking this around for almost ten years, we've never really needed the main floor heat but we're getting older and colder and I have a brand-new wood gasification boiler that will run better under more load. I wish I knew more about how this stuff worked, which is why I am here.

Does anyone have any photos of a compact, cleanly plumbed system that they can direct me to?

Also, on a side note - why would you combine black iron and copper in a heating system?


  • hot_rod
    hot_rod Member Posts: 16,532
    Do all the zones or loops require the same temperature? or within 15° of one another.

    Usually slab radiant requires a much lower supply than the staple up zones, do you have a load calculation and design for the system. that is really the best first step, before you start piping and pumping.

    The load calc will show how many BTU/ hr each room needs, the design will show loop lengths, supply temperature and required flow rates.

    Without this info it will be a guess, or trial and error approach.

    The thermal actuators on the manifolds don't really adjust temperature, they are mainly on/ off switches for the flow.

    You can adjust flow rates if then loops are different lengths, tab the manifold with the flow setters, but temperature will be the same across the supply manifold.

    What type of boiler? if you multi and micro zone a system you will get some short cycling of the boiler if it cannot modulate across the load range.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jon_E
    Jon_E Member Posts: 12
    All the zones and loops could be theoretically run at the same temperature. The slab zone (basement) would remain untouched. The manifold is in a good place and it works well. Everything else is staple-up tubing, and the loops are different lengths.

    My system is trial and error. I don't have any kind of load calcs for it.

    The boiler is constant feed - it's a wood-burning gasifier (Heatmaster G200) with a continuous flow of water through a plate exchanger ranging from 160 to 180 degrees. I'm not sure what my losses are in the main loop but the existing manifolds are getting water temps in the 120-140 degree range (set by mixing valves).

    Ultimately, my goal is to hook up the rest of the PEX loops without spreading my plumbing all over the place.
  • hot_rod
    hot_rod Member Posts: 16,532
    Hmmm, seems odd that you would send120- 140 to a basement slab, usually 90- 100 is adequate for that type of radiant.

    Regardless, it may be possible to use a single pump and zone valves or actuators for the various loops or zones. Without knowing the load for all the various zones it is tough to give you an answer.

    What type of boiler powers this system?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,355
    There are a lot of advantages to running fewer, bigger zones. As long as the rooms have similar heat loss characteristics, you should be able to combine them and simplify your system.

    When space is a concern, moving the pex manifolds to remote locations really helps clean things up. Pictures help.

    Room by room heat loss calcs seem intimidating at first but are not that hard. Download an app like the one slant fin offers and do some math. It is the only way to determine if the system is going to function correctly.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,514
    You say 120-140 degree supply temps. By multiple mixing valves. Are all mix valves set the same?