How to Install a RTH230B Thermostat to a Three Wire Connection

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The Honeywell RTH230B thermostat is electronic and programmable. It can be used to regulate the heat output from a furnace, central air conditioning or hot water system. This thermostat can control any of these systems if they have between two and five wires. In the case of a three-wire connection, the thermostat will control either a heating or cooling system--not both. Using a programmable thermostat for your home can make the system you are controlling more efficient, as it will stay at set temperatures during certain hours. This way, you will not be paying to heat or cool your home when no one is there, which is a real money saver.

Things You'll Need

  • Screwdriver
  • Masking tape
  • Pen
  • Pencil
  • Measuring tape
  • Wire strippers
  • Level
  • Drill
  • Drill bit
  • 2 Anchors

Turn off the power to the heating system or central air conditioning system via the emergency shut-off, or flip the breaker at the circuit panel.

Remove the old thermostat. Wrap a piece of masking tape around each wire. Write on the tape with a pen where it was connected to on the old thermostat. Wrap the wires around a pencil to prevent them from falling into the wall.

Measure the exposed wire at the end of each wire with the measuring tape to ensure there is 1/4-inch exposed. If there is less than 1/4-inch exposed, use wire strippers to remove the insulation from the outside of the wire. Insert the wire into the proper slot for the size wire you are stripping and squeeze the handles of the strippers together. Gently rock the stripper handles from side to side until the insulation is cut through. Slide the strippers off the end of the wire, taking the insulation with them.

Remove the faceplate from the new Honeywell RTH230B thermostat by snapping it off.

Expose the base plate by loosening the locking screw on either side of the Honeywell thermostat. Tilt the thermostat upwards.

Hold the base plate against the wall where it will be connected. Level the base plate to ensure the thermostat will be level after installation.

Mark the spots to drill for the anchors with a pen. Drill holes slightly smaller than the anchors being used, then push the anchors into the holes.

Remove the wires from the pencil. Pull the wires through the hole in the Honeywell thermostat's base plate.

Attach the base plate to the anchors with the screwdriver and screws.

Connect the wires to the Honeywell thermostat, utilizing the labels from when the old thermostat was removed. In most cases, the hook up will be the same. For a three-wire connection, you will have either a red wire, a white wire and a green wire or a red wire, a yellow wire and a green wire. "Rh" is the heating power supply terminal, "Rc" is the cooling power supply terminal, "W" is the heating signal terminal, "Y" is the cooling signal terminal and "G" is the fan terminal.

Connect the cooling system by connecting the red wire to the "Rc" terminal, the yellow wire to the "Y" terminal and the green wire to the "G" terminal. Connect the heating system by connecting the red wire to the "Rh" terminal, the white wire to the "W" terminal and the green wire to the "G" terminal. If your colors are different, go by the labels on the masking tape.

Remove the battery cover, install the batteries and replace the cover.

Connect the thermostat back to the base plate with the locking screws. Push the face plate back onto the thermostat.

Turn the power back on to the heating or cooling system.

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