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Thread: 2 wire heating system

  1. #1
    DIY Junior Member JJLJr's Avatar
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    Default 2 wire heating system

    I recently purchased a house and want to replace the Honeywell T87A 1000 thermostat with a programmable one. I purchased a Honeywell RTH6300B "5-2 Day" thermostat. When I removed the old t'stat, I noticed that there were only two wires, a black and a white. I traced the wiring back to the boiler and found a splice with the black connected to a red and white to white.
    Can I merely connect the existing black (red) wire to R and the white to W?

    Thanks for the help.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Yes. The fan on/auto switch will not work since there is not a wire to the furnace for its control, though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member JJLJr's Avatar
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    Is that a problem? I have an oil fired burner with forced hot water. How would the fan on/auto affect the system?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    That's probably why they didn't run more wires! The fan control is for forced air systems. It shouldn't matter at all. Note, some of the smart thermostats have internal switches to customize it to the type of heating system you have. If yours does, make sure to set them properly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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