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Line voltage Thermostat for Baseboard Hydronic Heat

Morrisnelz Member Posts: 1
edited October 2020 in Radiant Heating
We recently purchased a condo and realized that the previous owner has the wrong type of low voltage thermostat installed in a system that requires a 110V thermostat. This condo is in a co-op and the hydronic baseboard heating system receives hot water from boilers maintained by the HOA. (we have a thermostat in our home to control the heat on the main floor and it probably also controls the basement)

Ideally I'd like to upgrade to a smart thermostat but seems like Mysa won't be compatible with the system in our home as they do not work with baseboard heaters connected to an external heat source.

What model of thermostat would be best to replace this one currently in place :


  • Jamie Hall
    Jamie Hall Member Posts: 22,901
    Any good line voltage thermostat should work. Honeywell, Robertshaw and Lux -- at least -- all make suitable models. Some of them are at least programmable, if not 'net connected. Be quite sure that this really is line voltage, however.

    If it is, before you touch any wiring at all, be sure to shut off the power at the breaker and use a voltage tester -- for obvious reasons I prefer the non-contact type -- to be sure that the power is indeed off. The wiring shown in the second picture is, to be charitable, non-standard.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 9,410
    I'm curious what the 2 thermostats are connected to? It looks like that low voltage stat and the line voltage stat connect to different systems.
  • Zman
    Zman Member Posts: 7,542
    Posting some pictures of the heaters would help sort this out. I am guessing that you have an electric one in the mix somewhere.
    On the hot water baseboards, look for a zone valve tucked under the cover. A lot of larger buildings are set up that way.
    There are some slick relays that let you control the 120 volt system with a 24 volt t-stat. You need to be sure of what you have before proceeding.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein