As a regular reader/subscriber of our blogs and discussions, we’re sure you’ve come across multiple articles discussing how to make homes more energy-efficient. Among the many home improvements that will help you save money via energy savings, replacing an old thermostat with a new wifi thermostat or smart thermostat is right on top of that list. 

We’re going to take you through a detailed description of the process of DIY thermostat replacement.

Thermostat replacement: The process

Turning off the power

removing old thermostat
  • Turn off the power supply to your home’s HVAC system. Ideally, it ought to be clearly labeled in your main service panel and should not be difficult to find.
  • Double-check to make sure you’re installing the new thermostat on a circuit that corresponds to the highest voltage advised by the manufacturer. If the voltage is too high or short, you could seriously damage the controls and may even become a fire hazard.

Removing the old unit

  • Use a screwdriver to remove the cover plate on the old thermostat, exposing the mounting screws.
  • Unscrew the mounting screws to remove the thermostat body.

Labeling wires

  • It is important to label wires properly so you know which wire and which terminal belong together while attaching the new thermostat. 
  • Since there isn’t a standard color code, use alphabets to label the wires.
  • Disconnect the wires and either tape them to the wall or wrap them around a pencil to stop them from slipping into the wall cavity.

Checking if a C-wire is a needed

  • All smart thermostats use something called a C-sire, or common wire, for an uninterrupted supply of power only to the thermostat without turning on your fan or other gadgets. 
  • If you’re upgrading from one smart thermostat to another, a C-wire will already be present. However, if you are upgrading to a smart thermostat from a regular one, the C-wire may not be attached to the circuit.
  • In some cases, an unused C-wire may be stuffed in the wall, attached to the main service panel. Check, and if you find one, you can use this while installing the new device.
  • If there is no C-wire, purchase a power extender kit or an “add-a-wire” kit, and follow the manufacturer instructions on the box to add a C-wire.
  • Also, if your HVAC panel has an empty C terminal, install a C-wire yourself and run it to the thermostat through the walls.
  • If you’re not confident enough to handle the installation yourself, hire a licensed electrical contractor to handle the job for you.

Installing the new base and wiring

  • Loosen the mounting screws and remove the existing thermostat base.
  • Separate the new thermostat face and base. Screw in the new wall plate first.
  • Thread the low voltage wires through the corresponding outlets on the base plate.
  • Mount the base on the wall and use a level to make sure it is properly aligned.
  • Connect the low voltage wires to the corresponding screw terminals. Consult your new thermostat’s user manual to confirm you’re doing it right.
  • Make sure the remaining wires and sheathing are in good condition. Tighten any loose wires.
  • If the new device requires any batteries, now is the time to install them.

Read more: Smart home wiring

Mounting the new thermostat

turn off thermostat
  • To finish mounting the new thermostat base, gently push the connected wires gently into the wall cavity and plug it with a fire-resistant material such as fiberglass insulation.
  • Screw on the control unit to the base.
  • Restore power to the heating and cooling system. Then, clear the program memory by pressing the reset button.
  • Use the manufacturer’s instructions to program the new thermostat.
  • Test the heating and air conditioning systems to make sure the new thermostat works properly.

Read more: Small energy efficiency upgrades

Thermostat replacement pro tips

  • The process to install other types of thermostats, such as programmable thermostats, is similar to installing a wi-fi thermostat. However, always check manufacturer instructions to be safe.
  • Installation instructions for two-wire systems, i.e., those with only either heating or only cooling are different from the instructions mentioned above. Once again, refer to the manufacturer’s user manual.
  • If your home has more than one HVAC system, install a thermostat for each of them for optimal energy efficiency.
  • The average cost of a smart thermostat is between $250 and $300, with a range from as low as $100 to as high as $500.

Read more: Radiant barriers

DIY home improvements: Smart thermostat replacement was last modified: January 11th, 2023 by Narayan Shrouthy
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If someone had assured me that changing a thermostat was that simple, I would not have paid so much to a “professional”, or the second who had to fix the disaster of the first.