How to Install a Home Furnace Thermostat

The thermostat controls heating and cooling in your home. It comes in different styles such as Mercury Contact (older style), Mechanical Contact, Digital or Electronic Programmable but they all install basically the same.This tutorial will walk you through the steps involved in replacing your old thermostat with a new one, providing more convenient and accurate temperature control.

Selecting the proper type of thermostat is essential for your heating system to operate properly. If you have any questions about the correct type of thermostat to use with your furnace.

First you must disconnect and remove the old thermostat, being mindful as to the number and colors of the wires.


  • Shut off power to the furnace. You will find a circuit breaker or fuse that controls the furnace in the electrical service panel or fuse box. Find it and turn the circuit off by turning the circuit breaker to the “off” position or unscrewing the fuse.
  • Remove the old thermostat and expose the old wires.
  • It is a good idea to take a digital picture of the wires as they were connected to the original thermostat.
  • Disconnect the wires but be careful not to let them fall into the wall!
  • If they are not colored, label them as to which terminal they were connected.
  • Remove the old thermostat mounting plate from the wall.

Install New Thermostat Mounting Plate
Next, you install the new mounting plate.


  • Once the old mounting plate is removed, pull the old wired through the hole in the new mounting plate.
  • Place the mounting plate on the wall so that the wires come through the hole in the wall and through a mounting plate hole without binding the wires.
  • Using a torpedo level to level the mounting plate, mark two holes on the wall to fasten the mounting plate.
  • Install plate mounting screws, check for level then tighten screws.

Connect Thermostat Wires
Once the mounting plate is fastened to the wall, the next step is to connect the wires.


  • Match the color coded wires to the appropriately marked terminal connections on the thermostat and tighten to the terminal screws.
  • If the old wires had no color, connect them to the appropriate terminal based on the labeling you marked when you removed the old thermostat.
  • Refer to the digital picture you took if necessary.
  • Once the wires are connected, push excess wires into the wall.

Attach New Thermostat Cover
Once the wires are connected all that’s needed is to connect the new thermostat cover and set your controls.


  • Snap the new thermostat onto the mounting plate making sure the electrical connections are correctly seated.
  • Turn the electrical circuit back on that powers the furnace.
  • Set your thermostat to your desired settings