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How to replace an old Honeywell thermostat

Updated February 21, 2017

You are most likely familiar with the old Honeywell thermostat, especially if you are looking to replace one. The most commonly known old Honeywell thermostat is the manual round style thermostat. If you want to replace one, you should put in a programmable digital thermostat. These programmable thermostats allow you to have the thermostat automatically adjust the temperature up and down based on a program that is predetermined by you. The job can be done with only a few common hand tools.

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  1. Turn off the power to the HVAC system by locating the correct breaker in the circuit breaker panel and turning it off.

  2. Remove the cover of the old Honeywell thermostat by gently pulling it off. It will expose the wall plate where the thermostat wires are connected.

  3. Disconnect these wires and make note of what colour wire is hooked up to each labelled terminal.

  4. Remove the wall plate from the wall. Mount the new wall plate to the wall using drywall anchors and screws. Level it with your level before securing it tightly to the wall.

  5. Strip the thermostat wires to expose 6 mm (1/4 inch) of bare copper wire if needed and connect each thermostat wire to the new thermostat. Refer to the notes you made earlier to ensure that the wires are connected to the right terminals.

  6. Push the thermostat onto the wall plate by gently applying pressure until it "snaps" into place.

  7. Turn the power back on to the HVAC system. Read the instruction manual thoroughly for the thermostat you installed and program it to your desired settings.

  8. Tip

    Dispose of old Honeywell thermostats properly. Some thermostats contain mercury that needs to be deposited at a proper disposal site.


    The power needs to be off on the HVAC system when you replace the thermostat. Failure to do this may result in damage to the control board of the HVAC system.

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Things You'll Need

  • Screwdriver
  • Drywall anchors
  • Screws
  • Level
  • Cordless drill
  • Wire stripper

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