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2 stage thermostat with 2 24v transformers

gchristman
gchristman Member Posts: 21
edited November 2016 in Thermostats and Controls
I have both radiant and secondary baseboard heat. I have a taco zone valve controller for the baseboard heat and taco zone controller for the radiant pump. Each controller has its own 24v transformer and I need to get both of them to work with a single two stage thermostat. The thermostats I've seen only allow one 24v transformer, does anybody know of a thermostat that will work or a way to get the transformers to work? I'm trying to avoid 2 thermostats. Thanks.

Comments

  • Ironman
    Ironman Member Posts: 6,868
    If you parallel the transformers on both controls, you can run "W1" from the stat to the radiant control nod "W2" to the baseboard control.

    The problem that you're gonna have though, is that the algorithms in standard 2 stage stats are not design for radiant. Look at Tekmar's. I think it's model 549 or something near that that's 2 staged.

    You may just simply have to add a relay for the second stage.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Zman
  • Jamie Hall
    Jamie Hall Member Posts: 18,903
    Please don't parallel the two transformers. That sounds attractive, but unless they are perfectly matched which is unlikely you might get some real problems.

    Use a relay.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ZmanSolid_Fuel_ManHatterasguy
  • Zman
    Zman Member Posts: 7,328
    Ironman said:

    If you parallel the transformers on both controls, you can run "W1" from the stat to the radiant control nod "W2" to the baseboard control.

    The problem that you're gonna have though, is that the algorithms in standard 2 stage stats are not design for radiant. Look at Tekmar's. I think it's model 549 or something near that that's 2 staged.

    You may just simply have to add a relay for the second stage.

    Please don't parallel the two transformers. That sounds attractive, but unless they are perfectly matched which is unlikely you might get some real problems.

    Use a relay.

    These are both good suggestions.

    Technically, what Iron Man is suggesting will work, provided both transformers are exactly the same and wired to the same 120 volt power source. If they are wired to different phases, you will end up with 48 volts and something will smoke.

    I have also experienced what Jamie is cautioning you about where the 2 transformers were slightly different and the smoke came out of both of them.

    A relay would be the safe move.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,449
    I too would use a relay for the second stage. You can use ONE of the controls to power the thermostat and the first stage also goes to that same control. For the second stage the dry contacts of the relay go to the thermostat input on the OTHER control. This isolates the two controls from each other. You do not want two different transformers connected in any way in this type of situation.

    Taylor
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SWEI
    SWEI Member Posts: 7,356
    Add the relay or use a bigger transformer to power both.
    Hatterasguy
  • gchristman
    gchristman Member Posts: 21
    Could someone suggest a relay to use?
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,449
    Functional devices, RIBU1C is my go to. Will work on either 24v or 120v.

    Taylor
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    Hatterasguy
  • ratio
    ratio Member Posts: 3,173
    RIB relays are fantastically easy to use. I've taken to opening them up & nipping off the unused power leg, & usually the NC wire as well, to save space in the box and to make it harder to screw up the installation.
  • gchristman
    gchristman Member Posts: 21
    edited November 2016
    Would someone mind providing me with a simple wiring diagram for this application along with the recommend thermostat? I would like to be sure I fully understand it so I don't burn up anything. Thanks
  • ChrisJ
    ChrisJ Member Posts: 12,811
    edited November 2016
    I'm glad this thread was created.

    I've run into an issue where I want to control an air handler and my boiler using one thermostat that doesn't have an RC connection (VP TH8321U1097). It came as a huge surprise to me as all of the lower models have the RC connection.

    I figured using a relay for the boiler was the way to go but wasn't sure how acceptable in the industry or "normal" it would be. If someone else ever has to troubleshoot the system I'd rather things be appropriate.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ratio
    ratio Member Posts: 3,173
    A relay should be fine, but IIRC there's an R for the stat/cooling & an RH for the heat. Not necessarily an RC, but still the heat & cool can be separated. Is this the green backlight or the new white backlight?
  • ChrisJ
    ChrisJ Member Posts: 12,811
    ratio said:

    A relay should be fine, but IIRC there's an R for the stat/cooling & an RH for the heat. Not necessarily an RC, but still the heat & cool can be separated. Is this the green backlight or the new white backlight?

    Older green backlit one.

    All lower models have an RC and an R.
    This one, apparently, does not.


    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ratio
    ratio Member Posts: 3,173
    Huh. The universal relays use up all the terminals I guess. A RIB relay at the boiler, or an IDEC tucked into the wall maybe? ;) That'd keep him guessing!
    ChrisJ
  • ChrisJ
    ChrisJ Member Posts: 12,811
    ratio said:

    Huh. The universal relays use up all the terminals I guess. A RIB relay at the boiler, or an IDEC tucked into the wall maybe? ;) That'd keep him guessing!

    I'm glad you're as surprised as I was. :)
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment