2 wire heating system

Discussion in 'HVAC Heating & Cooling' started by JJLJr, Nov 5, 2007.

  1. JJLJr

    JJLJr New Member

    Messages:
    12
    Location:
    Rhode Island
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,156
    Location:
    New England
    Yes. The fan on/auto switch will not work since there is not a wire to the furnace for its control, though.
  3. JJLJr

    JJLJr New Member

    Messages:
    12
    Location:
    Rhode Island
    Is that a problem? I have an oil fired burner with forced hot water. How would the fan on/auto affect the system?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,156
    Location:
    New England
    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.
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