How to Replace Your Thermostat, Part Two: Installing a New Thermostat | Direct Energy Blog

How to Replace Your Thermostat, Part Two: Installing a New Thermostat

Welcome to the Take Charge of Your Home series from Direct Energy! Hiring a professional to perform household maintenance may offer convenience and peace of mind. You can do many of these jobs yourself with no experience or special tools. In the process, you’ll save money, learn about how your home works and gain a sense of accomplishment. A DIY task done well!

Last time, we took a look at two of the biggest decisions involved in replacing a thermostat: whether to replace your thermostat at all, and if so, which type to replace it with. Now it’s time to roll up our sleeves and get to work… or, alternatively, to pick up the phone and call a licensed installer.

Replacing a Thermostat: DIY or Hire a Pro?

As DIY electrical and HVAC projects go, swapping out one thermostat for another usually isn’t a huge job. The key word here is usually — in some cases, the wiring behind the existing thermostat isn’t an exact match for the new one, which can quickly make the job more complicated. If you discover damaged or degraded wiring when you remove the old thermostat, that could mean more trouble. And there are even cosmetic issues that can arise if your new thermostat occupies a smaller space on the wall than your old one, potentially leaving exposed holes that must be covered or patched.

On top of all those “ifs,” you should also have a basic understanding of electrical safety and some rudimentary experience with wiring if you’re going to attempt this installation alone. New thermostats typically ship with detailed instructions, and smart thermostats in particular tend to have customer support that is capable of walking you through tricky aspects of any installation. But if you feel completely out of your element installing one of these thermostats yourself, your best bet is to hire a professional to do the job right.

How to Replace Your Old Thermostat

Different thermostats have different wiring requirements and configurations, so until you know the exact layout of your existing wiring and your new thermostat, you can’t know the exact set of steps necessary to lead you through the project. You should always defer to the product installation instructions that ship with your new thermostat, and when in doubt, contact the customer support of your new thermostat’s manufacturer or call an HVAC installation professional to take over the task.

Things you’ll need:

  • Smart thermostat
  • Screwdriver (flat or phillips head depends on the type of screws connecting your old thermostat to the wall)
  • Digital camera or phone
  • Masking tape

These steps outline the typical workflow of DIY thermostat replacement:

  1. Shut off the power to your air conditioner, furnace, heat pump and any other HVAC equipment at your circuit breaker box.
  2. Remove your old thermostat from the wall. With most models, this can be done without tools by sliding the unit off the wall plate or squeezing plastic tabs to release it. If you need customized instructions for this step, refer to your original thermostat documentation or search for the manual online using the manufacturer name and product number.
  3. Take a clear photo of the wiring configuration behind your existing thermostat. You may need to refer to this photo throughout the installation process to see which color wire is associated with each terminal, and if you encounter trouble during the installation process, the photo will help you reconnect your old thermostat in the meantime.
  4. Check to see if the connected wires in your old thermostat match the wiring requirements of your new thermostat. Don’t rely on wire color to correspond with the terminal letters; use your photo from the previous step to match the wires to their corresponding terminals on the new thermostat. Older thermostats may not have a connected “C” wire, but many smart thermostats require this connection to maintain a continuous flow of electricity. If you have a connected “C” wire, skip to step six.
  5. If you do not have a “C” wire connected to your thermostat, there may be a live “C” wire tucked into the wall. If you can pull one or more disconnected wires through the wall cavity, note their colors. Then remove the control panel cover on your furnace and look for a series of colored wires connected to terminals with labels that match the terminals on your thermostat. If there’s a wire connected to the “C” terminal on your furnace that matches the color of one of the wires you pulled through the wall, you can connect that wire to the “C” terminal of your new thermostat. If there is no wire connected to your furnace’s “C” terminal, you may need to run a new wire, which is a job best left to a licensed electrician or HVAC technician.
  6. Disconnect the wires from the base of your old thermostat. Tape them to the wall to prevent them from falling into the cavity.
  7. Remove the old thermostat wall plate.
  8. Install the new thermostat wall plate. This is often the trickiest DIY step because of differences in sizes and mounting screw configurations among different thermostat models. With luck, you might not need to do much to make your new thermostat fit well and look great. But if you have a mismatch, you may need to install new drywall screw anchors or even patch in new drywall.
  9. Reconnect the wires to the appropriate terminals on the new thermostat wall plate. Refer to your photo as needed.
  10. Connect your new thermostat to the wall plate.
  11. Restore power to your HVAC system at the circuit breaker box.
  12. Configure your new thermostat.

If you’re lucky enough to have all the necessary wiring in place and your new wall plate is an approximate match for the old one, this could be a simple 30-minute job. If you need to run new wiring, patch drywall and repaint, it could be a weekend project. You won’t really know what you’re getting into until you know your current wiring configuration and see how everything matches up with the requirements of your new thermostat.

When in doubt, refer to your photo and reconnect everything as it was before turning the project over to a pro.