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Using existing 14 ga wire for low voltage tstat

I just put in a new boiler and am using the Taco SR506-EXP-4 switching relay. I have 6 zones including indirect water heater. One zone is and old line voltage mercury tstat that is hooked up direct to circ. I'd like to change that to a low voltage tstat and use the panel to control circ. Yes I will make sure it is not hooked up to 120v.
My question is....can i use the existing 14 ga wire for the run, changing to 18 ga wire in a box near the panel and in the box behind the tstat? It would be difficult to fish a new wire to the basement.


  • Jamie Hall
    Jamie Hall Member Posts: 22,175
    You can always use a bigger wire in place of a small one. Two things to look for, though. The insulation needs to be in decent shape, and any fusing needs to correspond to the smallest wire in the line. You may find that you need to add a smaller gauge wire at the thermostat to fit its connections.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Spark949_
    Spark949_ Member Posts: 8
    And now I need a simple thermostat that will cover the box on the wall. Any suggestions?
    JUGHNE Member Posts: 10,914
    If the box is mounted horizontally most Tstats will fit on that.

    If vertical most Tstat companies offer cover up back plates.
    EBEBRATT-Ed Member Posts: 14,560
    If you cant find an adapter cover you can also cover the box with a blank electrical box cover, drill a hole in it for the thermostat wires. Use a bushing so the wires don't get cut and mount the thermostat on top of that
    HVACNUT Member Posts: 5,479
    The new Honeywell P6 comes with a large back plate if needed and can be set up for "no program". Good price too.