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Dual Thermostats - Tell me it isn't so.

Greetings Control Pro's,

I've got an interesting challenge that I am sure someone has a solution for. Redoing an older home with new boiler and five new forced air units. Three of the zones have radiant ceiling heat. Since there is so little cost difference, we are using heat pumps for cooling and secondary heat source. One of the zones has such a small heat gain, we are forced to use a mini split heat pump with the compact ducted air handler.

The problem is, mini split units use proprietary thermostats because the inverter compressors.(Sometimes I think Mini-Split controls are a prank from the Japanese because they lost the war.) So how do I use one thermostat to control the radiant (via circulator relay) and the mini split unit?


  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    Save a little money.

    Turn the MiniSpilt off while using the radiant. It has no reason to be on.

  • Housedoc
    Housedoc Member Posts: 66
    Still need two thermostats

    Okay with that Harvey. But we still need two thermostats
  • icesailor
    icesailor Member Posts: 7,265


    Can't one be set lower than the other and make that one proprietary?
  • Housedoc
    Housedoc Member Posts: 66
    Still two

    That's still two
  • Big Ed_4
    Big Ed_4 Member Posts: 2,377
    Red Link

    i understand Mitsubishi units can be Honeywell Redlinked which may give you a one thermostat option, Thinking but never looked into it but surprised if not offered by now if mini splits interfacing to a central computer control system ...
    I have enough experience to know , that I dont know it all
  • Housedoc
    Housedoc Member Posts: 66
    You Are Correct

    You are correct Ed. The Mitsubishi mini split made a deal with Honeywell to build a "Focus Pro" twin that talks Japanese. It is the best choice for controlling the Misubishi unit. And it does connect to Redlink. But it is disappointing that it will not support conventional R-W-Y controls. It also will not read humidity. So I am not encouraged it will control anything but the Mitsubishi unit.

    Perhaps my best solution may be to hide the radiant control to avoid confusion. Then allow the owners to operate wall thermostats for cooling and whatever heating they want. I invision using sensors without any adjustment, except through a central controller. Set the radiant on 68 degrees of so and let it fly. Then the owner can adjust the forced air thermostats all they want.
  • icesailor
    icesailor Member Posts: 7,265
    Good Plan:

    Sounds like a very good plan.