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Two thermostat connections to same circulator pump possible ?

moots Member Posts: 37
Hi Folks:

So I have a circulator pump per zone activated by thermostats (see photo). Is it at all possible to have a pair of thermostats activating the same zone when calling for heat maybe some sort of master/slave scheme ? Or will the pump simply run based on whichever thermostat is used at a given time ?




  • ratio
    ratio Member Posts: 3,623
    If the thermostats share the same R wire ( & C if it's there), no reason why the can't share the W (output of the stat). The pump will run when either or both stats call for heat. Is this what you want?
  • 109A_5
    109A_5 Member Posts: 1,385
    With the information given just put two plain old thermostats in parallel. So either can call for heat in that zone. For master / slave or priority you would need some logic with relays or other equipment, don't know what the benefit would be to a master / slave scenario.

    Are different parts of that zone's area colder at different times ? If not maybe just move the thermostat.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,818
    edited August 2022
    I'm not seeing a good reason to do this. @moots needs a basic understanding of the function of a thermostat. The location of a thermostat does not make more heat happen in the area of the thermostat. If you want to put another thermostat in a room in order to get more heat in that room, that might work, but the other rooms that may be just fine will also operate longer. The area you want warmer will get warmer but the other areas that will get too hot as a result will not get colder no matter how low you set the thermostat in the other room.

    Think of a thermostat like a light switch that works on temperature. byt the switch works every light in the zone. If any switch is turned on the light will illuminate any room that has a light fixture controlled by that switch. You can't turn off the other switch in the other room and expect the light to only go in the room you want it. That is why there are separate switches for each light in each room. You can't just add a switch to make the light go where you want, or a thermostat and make the pipes move the water somewhere else. You need to start with the design you want and make the piping do what you want.
    moots said:

    the pump simply run based on whichever thermostat is used at a given time ?



    what you said here is what will happen

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • moots
    moots Member Posts: 37
    edited August 2022
    The original idea was to expand an existing zone to an apartment that I want to rent out. The part of the zone resides in the main house. The renter can control his heat with an additional thermostat but when he leaves I can dial it down from the main house. So thanks to Ed it's not a good idea to mix radiant and fin tube heat on the same zone without a mixing valve. So the solution is to create a new zone for my apartment which unfortunately means modifying a few things. I would be happy to call a pro in but in the Colorado Mountains none are available for some time. Thanks everyone !
  • HomerJSmith
    HomerJSmith Member Posts: 2,435
    You bet! It's just the one that has the highest setting that will control.