So you just went out and bought a smart thermostat, and now it’s time to install it. Don’t let the thought of wiring and circuit breakers scare you. The process is easier than you think, and Consumer Reports is here to help.

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Before you dive in to the project, make sure your thermostat is compatible with your system and wiring. (For example, the Nest Thermostat E won't work with two-stage heat pump systems.) Certain manufacturers, including EcobeeHoneywell, and Nest, offer compatibility tools or checklists online to help you make sure their models will work with your wiring. 

Our thermostat test engineer, Peter Anzalone, also has some tips. "Make sure you aren’t replacing your thermostat during a time when a functioning HVAC system is important, such as during a particularly cold winter or shortly before guests will be staying with you for a holiday," says Anzalone. "And don't toss the old thermostat. If you mess things up or can't get the new thermostat to work, you can always reconnect the old one."

If you run into trouble at any point during installation, we strongly encourage you to consult an electrician or HVAC technician. The last thing you want to do is bust your HVAC system—it will cost a lot more to fix a shorted-out air handler than to install a thermostat.

Below you’ll find our general installation guide. It might vary slightly from manufacturer instructions for your specific thermostat, so be sure to review the installation guide and/or owner's manual.

With all those caveats out of the way, it's high time to get started.

1. Turn Off Your HVAC System

Turn off your HVAC system at the circuit breaker

Before you remove your old thermostat, turn off your entire HVAC system at the breaker panel. (Your system might have multiple breakers.) This will cut power to your thermostat and keep you from accidentally shorting electrical components of your system when you’re working with the wires at the thermostat.

Some older, battery-powered thermostats might still appear to be on even though the system is powered down. Honeywell recommends trying to turn the system on at your thermostat and listening for signs of your system running to make sure that everything is actually off. 


2. Pop Off the Faceplate

Pop off the old thermostat's faceplate

You’ll need to remove the faceplate of your old thermostat to get at the low-voltage wiring and backplate. It should pop right off with a little bit of effort. If it doesn’t, don’t force it—there might be a hidden screw or two that you need to remove first (look underneath). If not, consult your electrician or HVAC tech.

Take a photo of the wiring with your smartphone so you have a record of which lines connect to which terminals. Some thermostats also include stickers to label the wires with the codes on the terminals. Place them before you disconnect the wires. 


Check our 
comprehensive smart thermostat ratings to find the right smart thermostat for your home.


3. Remove the Backplate

Remove the thermostat backplate

Now it’s time to remove the thermostat wires from the backplate. Depending on the model, you might need to back out small screws that hold the wires in place, or press small tabs using a pen to release the wires. For the backplate, simply use a screwdriver to remove the screws holding it on the wall. 


4. Add a C-Wire (Optional)

Add a C-wire if needed

If your system already has a C-wire, you can skip this step. If it doesn't, you might need to add another wire to serve as the common wire, which powers the thermostat. "We recommend using a C-wire since this is the most straightforward way to provide power to your smart thermostat," Anzalone says.

Some thermostat makers, like Ecobee, include an adapter with their smart thermostats to add a C-wire. Your other option is to buy and install a third-party "add-a-wire" adapter. These adapters come with specific instructions, and we recommend following them to the letter.

Note: If you are not comfortable adding a wire, we strongly recommend hiring an electrician or HVAC technician to install the common wire, as you risk damaging your system. 


5. Use the New Backplate as a Template

Use the new backplate as a template

Use the new thermostat’s backplate and a pencil to mark the wall. Using a small bit, drill holes at the marks for the backplate screws. (Install wall anchors if necessary.) Be sure to pull the thermostat wires through the backplate before screwing it into the wall. 


6. Reconnect the Wires

Reconnect the wires

Once the backplate is securely attached, connect the thermostat wires to their corresponding terminals. If you labeled your wires with stickers, this step should be very straightforward. If not, consult the photo of the wiring on your old backplate to match the wires to their terminals.


7. Install the New Faceplate

Install the new faceplate and turn the circuit breaker back on

With the wiring in place, you should be able to snap the faceplate of your new thermostat onto the backplate. If it doesn’t attach easily, don’t force it since wires could be in the way. Tuck them back into the wall before trying to attach the faceplate again.

Now you can turn on the breaker for your HVAC system. This should restore power to the thermostat, which will begin to boot up. (Yes, smart thermostats boot up just like your laptop.) 


8. Connect the Thermostat to WiFi

Connect the thermostat to WiFi and finish setup

Now that your new smart thermostat has powered on, it will likely take you through a series of prompts to connect it to WiFi and set up its companion smartphone app. This part of the process can differ depending on the make and model, so follow the prompts closely.

With your new smart thermostat ready to use, you'll start saving money.




Want to find the right smart thermostat for you? Check out our comprehensive smart thermostat ratings.