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How to Wire a Thermostat

Replacing a thermostat can improve your home’s energy efficiency. An older thermostat can lose its sensitivity to temperature changes. That results in erratic heating and cooling. If you don’t have a programmable thermostat, you’re missing opportunities to optimize heating and cooling. All that stands between you and a new thermostat are the following steps for how to wire a thermostat. Oliver always recommends consulting with or hiring a licensed electrician before doing anything with your home’s electrical system.

A programmable thermostat is just the starting point for home automation. Smart home systems improve both energy efficiency and security. Technicians from Oliver install automation systems that manage appliances, locks, lighting, and heating and cooling.

Required ToolsHow to Wire a Thermostat

  • Screwdrivers
  • Camera phone
  • Painter’s tape
  • Marker
  • Pencil
  • Level
  • Power drill
  • Magnifying glass, optional

Overview of Thermostat Wiring

Before wiring in a new thermostat, you should learn about the different wires you’ll find once you take off the cover plate. You’ll have to match up each wire coming out of the wall with the correct port on your new thermostat. The most important first step is always to turn off the power to your thermostat and HVAC system.

  • White wire connects to the heating system.
  • Yellow wire connects to the AC compressor.
  • Green wire connects to the fan.
  • Red (Rc) wire provides power to the cooling system connection.
  • Red (Rh) wire provides power to the heating system connection.
  • Common or “C” wire provides power to the thermostat. (C wire is most often blue but may be purple, brown, or black.)
  • Orange wire connects to the heat pump, if present.

These wires are mostly standardized, but you could encounter variations. If you open up your thermostat and can’t tell which wire is what, ask an expert at Oliver to wire in the new one. It’s vital to get the Rc and Rh wires in the right spots. This step can be confusing due to both wires being red.

How to Wire a Thermostat Step by Step

  1. TURN OFF YOUR POWER AT THE BREAKER
  2. Remove the existing thermostat cover plate. You might have to undo a screw, or the plate might just pop off.
  3. Set the thermostat to OFF. Make sure the furnace or AC stops before proceeding.
  4. Go to your breaker box and shut off electricity to the heating and cooling system.
  5. Take a look at the wires in the old thermostat. See if you can identify them based on the guidance above.
  6. The letters and labels on the old wiring plate can be tiny. You might want to use a magnifying glass to look for details.
  7. Look first for the C wire. Programmable thermostats must connect to this power supply. Old thermostats did not necessarily need a C wire.
  8. If you don’t see one, look behind the wiring plate. A previous installer might have tucked one out of the way.
  9. If you can’t find a C wire, consult an electrician.
  10. Presuming you found the C wire, you can proceed.
  11. Go through the wires and label them with a bit of tape and a marker.
  12. Take a picture of the wiring with your phone before disconnecting everything.
  13. With a screwdriver, loosen the mounting screws and pull the wires free.
  14. Slip the old wall plate off.
  15. Tape the wires to the wall because they could slip down the hole into the wall.
  16. Position the new thermostat plate on the wall.
  17. Use a level to make sure it’s not crooked.
  18. Mark new screw holes through the plate with a pencil.
  19. Drill holes and insert anchors.
  20. Pull the wires through the new wall plate.
  21. Drive in the screws to secure the plate to the wall.
  22. Connect the wires to the correct ports on the new plate.
  23. Check your work against the picture that you took of the original wiring.
  24. Put on the thermostat cover.
  25. Restore power to your heating and cooling.
  26. Turn the thermostat ON.
  27. Consult the manufacturer’s directions for programming it and setting up Wi-Fi if needed.

Hire a Professional Electrician and HVAC Expert

Heating and cooling systems are finicky. Any errors with how to wire a thermostat will make your system malfunction. For best results, have our licensed technicians install your new thermostat. If you’ve already installed one, this is a good opportunity to get your system checked out. We can confirm that the thermostat is functioning properly and tune up your furnace or AC while we’re there. Routine, seasonal maintenance supports energy efficiency and extends the lifespan of the equipment. Having HVAC professionals attend to your heating and cooling equipment is always best. Contact Oliver today.

Need help with this project?

If you do not have the time, tools, or experience necessary to complete the project, please contact the professionals at Oliver for help.

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