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wm97+ controlling two different radiant installation methods

I'm leaning toward buying a Weil-Mclain 97+ 110ct 88k btu boiler for my upcoming radiant install.  Does anybody know if the onboard controls can do two seperate temps?  I will have one underfloor radiant installation for my main living floor and another installation above the ceiling drywall on our top floor (accessable via the attic so to not have to rip down finished ceilings/floors anywhere). 

These zones should have (roughly) parallell heating curves, but i know the ceiling installation will require higher temps to meet demand. I want to run two manifolds with zone valve control and use one circulator per manifold.  I need to mix the water with cooler water in the main floor using some sort of mixing valve...or can the wm97 do that as well?

anybody familiar?  this is my first experience with this stuff.  i looked through the manual but couldn't find anything specific.  it states it can control up to three zones.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Weil-McLain have their installation manuals on line in .pdf form. I suspect, based on my W-M Ultra 3 that they can handle this. They sure do for me. 1 indirect, one radiant, one baseboard.
  • Boiler wrestler
    Boiler wrestler Member Posts: 43
    You can have one space heating temperature and one domestic with the WM97. The domestic temp would not react to outdoor reset.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    It looks to me that, according to page 66 of the installation manual, that there are three thermostat inputs on the WM-97 boilers. Zone 1 is normally used for Indirect Fired Domestic Hot Water Heater.

    Zone 2 is for space heating.

    Zone 3 is for space heating.

    The zone number is the priority. So domestic hot water has maximum priority, and the others are lower priority in the obvious way.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    avionator Did you get your answer? I have a similar system as you describe, using a W-M Ultra 3 whose controls are quite similar to the WM-97. I use three different reset curves: one for the indirect domestic hot water heater, one for a radiant slab at grade, and one for a baseboard zone with oversized baseboards.

    The indirect does not really reset at all. When it runs, it achieves 175F (default is 190F). The radiant slab runs between 76F and 128F, and the baseboards run between 110F and 140F.

    Since the boiler can produce one temperature at a time, what I do is set up the timers so the highest priority runs first, and can run for only 30 minutes before it yields priority to one of the other demands. Since the indirect almost never runs over 15 minutes, and sometimes under 10 minutes, this does not affect the hot water, and does not interfere with heating the house very much. I think it runs 2 or 3 times a day.

    The heating zones are set up to take turns, the slab zone gets 35 minutes in an hour and the baseboard gets 25 minutes if both are demanding heat the whole time. For my system, this works just fine. The radiant slab zone runs for very long times (hours) and the baseboard does not. Actually, the baseboard gets some heat even if the slab zone has priority because I sent the lower temperature water through both the slab and the baseboards when that happens, so the baseboard zone will get some heat. If your loads are not like mine, you will probably need to have a temperature reducing valve to drive the radiant zone so both can run at the same time as needed. Use an electrically controlled valve so it can use reset too.