Proper ecobee3 wiring for PEK users

How to Install an ecobee3 Smart Thermostat 73

ecobee3 retail box - coming to a shelf near you!

So you got your hands on an ecobee3 smart thermostat, and instead of reading through the installation manual (which is actually pretty good), you came to the Internet to figure out how to install your ecobee3.

OK, fine… I’ll help you. 🙂

This how-to guide for installing your ecobee3 covers a few different basic install options. Depending on  what type of thermostat you’re replacing, and how many wires are available to your old thermostat, there’s a good chance that following these steps will get you up and running quickly with your new ecobee3.

However, I want to be clear that this how-to only discusses the most common install scenarios, which should cover the vast majority of homeowners’ needs. However, if your install is more complex, or you run into any trouble along the way, I recommend you contact ecobee’s tech support, or stop by the SmartHomeHub community forums and get some peer support in the ecobee section.

Finally, if you’re upgrading from an original ecobee Smart Thermostat, I’m writing a separate installation post just for you. Stay tuned. 🙂

Before You Start

Before you start, you’ll definitely need a Phillips head screwdriver. You might need a small flat head screwdriver, depending on how your old thermostat is connected. You’ll probably also need a drill to help install drywall wall anchors when it comes time to attach your ecobee3 to the wall.

This might also be the perfect time for me to inform you that by doing this project yourself, you assume all risks associated with it. I think that pretty much anyone can install one of these bad-boys themselves… even if they’ve never done anything like it before. But if, after reading through this how-to, it still sounds like something too far out of your comfort zone, any half-decent HVAC professional should be able to get this installed for you in well under an hour. Seriously,  don’t try to let them convince you it’s a major job… it’s really not — and you can tell them I said so. 🙂

Step 1: Kill the Power to your HVAC

The first step in any DIY project that involves any sort of power (even a “relatively” low voltage such as 24V), is to kill the power. If your furnace has a light switch nearby that doesn’t actually turn off any lights, that’s probably the power switch for your furnace. If you don’t have a switch, just throw the breaker (or breakers, if there’s more than one) that power your system.

Step 2: Understand A Little About Thermostat Wiring

Even if you don’t know anything about thermostat wiring, you can learn pretty much everything you need to know in the next 30 seconds. Your thermostat is basically a fancy “switch” that tells your furnace, heat pump, or A/C (I’ll refer to all of those as simply your “HVAC system” from now on) when to turn stuff on and off. Different wires from the thermostat control the different functions (heat, cool, fan) of your HVAC. The most common wires are:

  • R (Red) = Main Power. Technically, it connects to the “hot” (as in “powered”) side of your system’s transformer.
  • W (White or Orange) = Heat. This switches on the gas, oil, or electric heat. Sometimes, you might also see numbers with it (such as W1 and W2), which is HVAC units with more than one heating “stage.”
  • G (Green) = Fan. This controls the blower that forces air through your system.
  • Y (Yellow) = Compressor. If you have an air conditioner or a heat pump, this switches the compressor on that unit on and off.
  • C (Blue) = Common. This connects to the “common” side of your transformer (in four-wire systems, the blue common wire will not be connected).

Ideally, the HVAC professional that installed your system used standard colored thermostat wire, and connected the wires to the terminals that match the wires’ color. But that’s not always the case. Throughout this guide, the actual color of the wire is not what’s important. What’s important is what terminal that wire is (and was) connected to on both ends of the wire. So keep that in mind as you read, and don’t forget to snap photos and label things as you go.

Step 3: Remove Your Old Thermostat

Carefully remove your old thermostat from your wall, but don’t unhook any wires yet. Depending on what type of old thermostat you have, you might need to pop off a cover to access the mounting screws underneath. Be patient, and if needed, search online for instructions on removing your particular model. Before you start disconnecting any wires, however, snap some photos showing how the existing wires are connected to your old thermostat. If anything goes wrong, and you want to hook it back up, you can refer to the photo later (this is a good idea to do before disconnecting anything).

As you first inspect your old thermostat’s wiring, be on the lookout for the “C” wire. In order to install an ecobee3, you’ll need a “C” wire — either an actual one, or a “virtual” one (more on that later).

When you’ve exposed your thermostat’s wiring, if your original installer did things right, the color of the wires will match the letters on the wiring terminals. If done ideally, a 4-wire install would look something like this:

4 Wire Thermostat Wiring

4 Wire Thermostat Wiring

Notice that the terminals I talked about earlier are connected to wires that match the color: red to R, green to G, yellow to Y, and white to W. That makes things easy, but that might not be the case with your thermostat. If the colors of your wires don’t match the letters on the wiring terminals, don’t worry. In your ecobee3’s box, there’s a sheet of stickers for labeling your existing wiring. Before you disconnect any wires from your old thermostat, label all the wires (based on the terminal to which it’s connected, not the actual wire color) using the stickers on that sheet. Double check to make sure everything is labelled correctly before disconnecting any wires.

Once you’re certain, go ahead and disconnect your old wires and put your old thermostat aside. The wires coming out of the wall should look something like this:

Do you have four thermostat wires or five?

Do you have four thermostat wires or five?

Notice in the above picture that I have five wires available: red, blue, yellow, green, and white (although it’s not uncommon to sometimes see an orange wire instead of a white one). However, I actually only had four wires connected to my old thermostat. The blue one was just coiled up and unused (which isn’t that rare), and my old thermostat didn’t need a “C'” wire to operate. However, the ecobee3 requires a “C” wire to be powered properly, so even though I didn’t have a “C” wire connected to my old thermostat, I do have a spare wire that I can use a the “C” wire for installing my ecobee3. So if you also have four wires connected to your old thermostat, but have a spare wire in the wall, label everything and skip down to Step 4-and-a-half.

It’s possible that when you pull the cover off your old thermostat, it could look this one from my Utah house:

Existing Thermostat

Notice that this example has six wires connected: the blue wire is connected to W2 (because I have a 2 stage furnace there) and the orange wire is being used as the “C” wire. That’s fine — as long as all the wires are properly labelled based on the terminals they’re connected to before you disconnect them. If yours looks like this, label them and skip to Step 5.

Basically, if your old thermostat has a wire connected to its “C” terminal, label all the wires, disconnect everything, and skip to Step 5.

If your old thermostat didn’t have a “C” wire connected, but you have an unused wire in the wall that you could use as a “C” wire, label everything and skip to Step 4-and-a-half.

Finally, if you have only four wires coming out of your wall, and none of them were the “C” wire, don’t worry! Your ecobee3 comes with a Power Extender Kit (PEK) included, which creates a “virtual” C wire using your existing wiring. Follow Step 4 to install the PEK before moving on.

Step 4: Install the ecobee Power Extender Kit (PEK)

You should follow this step only if you don’t have a “C” wire connected to your old thermostat, and also don’t have a “spare” wire available to use as the “C” wire. The most common example of this would be if you only had R, G, Y, and W wires at your thermostat.

This step also requires you to crack open your HVAC system and connect something to its main control board. Relax, it sounds way scarier than it actually is. As long as you’ve killed the power to your HVAC, you’ll be fine. However, if the thought of that still freaks you out, contact ecobee’s support crew, or hire a professional to install your ecobee3 for you. The PEK section in the installation manual that came with your ecobee3 also does a great job of explaining how to do this step.

In cases where you only have four wires available, the PEK (which is included with your ecobee3) will create a “virtual” C wire to help reliably power your ecobee3 thermostat. The ecobee3’s PEK looks like this:

ecobee Power Extender Kit

ecobee Power Extender Kit

Those five white wires in the above photo (labelled R, C, G, W, Y) connect to your furnace’s control board, and the four wires coming from your thermostat location connect to the other end of the PEK.

To wire it up, remove the cover from the PEK, and look inside:

Inside the ecobee PEK

Inside the ecobee PEK

I recommend checking to make sure the five wires on the top are screwed in snugly (but don’t over-tighten them).

Next, go to wherever your HVAC system is located in your house (probably the basement, garage, or a utility room) and double-check to make sure your furnace is powered off. Then remove whatever panels you need to in order to access the control board (you might have to search online or check your owner’s manual to find out how).

The control board should look something like this (this is at my Seattle house):

HVAC control board

or this (this is at my Utah house):

Existing Furnace Wires

of maybe this (this is the furnace at my cabin):

Cabin Furnace Wiring 1
Don’t worry if your wire colors don’t match exactly, or if there are maybe more wires than you were expecting. Other components (such as fan timers, or wires that run to a condensate pump. etc.) might also be wired here (which is the case in all of the above photos). Focus on locating the four wires that are currently running to your thermostat location. They’ll almost certainly be attached to the R, Y, G, and W terminals on the control board. They’ll eventually group together and head off toward your thermostat location.

Loosen the terminals for those four thermostat wires, then disconnect the wires. If there are other wires attached to the same terminals on the control board, leave those other wires connected. You should only remove the four wires that run to your thermostat location.

Next, connect the five white wires (with the colored labels) from the PEK to your HVAC’s control board terminal that matches each wire’s label (R, W, Y, G, C). Again, if there are other components already connected to those terminals, make sure they also stay connected, so that whatever they’re controlling will continue to work. Be careful when tightening down the terminals. You want them snug enough to hold the wires in place (gently tug on the wires to make sure they won’t come loose easily), but don’t over-tighten them and break something.

With one side of the PEK wired to your control board, connect the four wires coming from your thermostat location to the appropriate terminals in the PEK’s cover, like this:

Standard 4 wire thermostat connections go in this side

Standard 4 wire thermostat connections go in this side

Make sure you connect the four thermostat wires so that they match your labels back at the wall… even if the wire colors don’t match (in the above example, the wire colors do happen to match).

When you’re done connecting all the wires, snap the lid back on the PEK, then mount the PEK somewhere “safe” inside your HVAC unit (there should be some double-stick tape in your ecobee3 box). Make sure it’s mounted somewhere dry, and where the cords aren’t being strained or at risk of getting caught in a fan or any other moving part. Once your PEK is wired and mounted, go ahead and close up your HVAC unit, then move on to Step 5.

Step 4-and-a-Half: Connect the Unused “C” Wire  to your HVAC Control Board

You only need to follow this step if your old thermostat didn’t have a “C” wire connected to it, but you were lucky enough not to have to use the PEK because you have a “spare” wire available in your wall. Chances are that if the spare wire wasn’t connected at the thermostat end, it’s probably not connected on the other end (at your HVAC control board) either. So I called this Step 4-and-a-half because it’s kind of like Step 4 in that you need to remove the panel(s) on your HVAC system and access your control board, but you won’t need to do anything else except locate and connect your “spare” wire to the “C” terminal on the control board.

So skim through Step 4, open your HVAC unit, locate the wires coming from the direction of your thermostat location, trace them to the control board (the other wires in that bundle will already be connected to the control board), then connect the “spare” wire (mine happened to be blue, but yours could be any color) to the “C” terminal on your control board. You may have to strip the end of the wire to expose the copper inside before you attach it. If something else is already connected to the “C” terminal, keep it there and wire your spare to it as well.

When you’re done, close up your HVAC unit and head back to your thermostat location. You might also have to strip that end of the spare wire, too. Now that you have five wires connected to your HVAC system, you’re ready to move to Step 5.

Step 5: Install the ecobee3 Back Plate

Depending on how ugly your wall looked when you removed your old thermostat, you’ll need to decide whether to use the standard trim plate when mounting your ecobee3 to the wall, or the larger trim plate — to hide holes, missing paint, or other hideous things. I decided to use the larger plate on my first install, until I can get around to filling the old thermostat’s mounting holes and touching up the paint.

Connect your trim plate of choice to the ecobee3 back plate (the back place is the piece with the wiring terminals on it), thread your thermostat wires through the round hole in the middle, then press the whole thing up against your wall. Use the built-in level to make sure it’s straight, then mark the two mounting screw locations.

If you need to use drywall anchors for your install (and you probably will), remove the back plate and install them now on your marked locations. Then re-thread the wires through the hole in the mounting plate, line up the back plate on the wall, and attach the top screw, like this:

ecobee3 top mounting screw attached

ecobee3 top mounting screw attached

With the top screw attached, you can swivel the unit to line up the level bubble between the markings, and then attach the bottom screw.

Step 6: Connect the Wires

If you installed the Power Extension Kit (PEK), you need to connect your four wires to the ecobee3 back plate like this:

  • R wire to Rc terminal (PEK installs must use the Rc terminal)
  • G wire to G terminal
  • Y wire to Y1 terminal
  • W wire to W1 (Aux1) terminal

Again, my wire colors in this photo happen to match up, but make sure to attach the appropriately labeled wire, even if it’s not the matching color. When wired properly with a PEK, your ecobee3 back plate should look something like this:

Proper ecobee3 wiring for PEK users

Proper ecobee3 wiring for PEK users

If you didn’t need the PEK, then simply connect all your labelled wires (including the “C” wire) to the matching terminals on the ecobee3 back plate. Your “R” wire can connect to either the Rc or the Rh terminal, because the ecobee3 will automatically “bridge” these two terminals (unless you used the PEK, in which case you must use the Rc terminal).

My standard 5-wire installation looks like this:

Standard 5-wire connections to the ecobee3

Standard 5-wire connections to the ecobee3

You might have even more wires, such as Y2 or W2 or O/B. As long as you connect them up to the same terminals as your old thermostat, you’ll be good to go. Your ecobee3 installation guide has diagrams of some of the more advanced wiring options, if needed.

Step 7: Plug In and Power your ecobee3

It’s the moment you’ve been waiting for! Time to see if you get to victoriously thrust your hands in the air… or if you’re running for the fire extinguisher to put out the flames. I kid! I kid! There probably won’t be any flames.

Carefully slide the main ecobee3 unit into the back plate, until it “clicks” into place. You shouldn’t have to force it, so if it’s not going easily, check to make sure you don’t have wires sticking too far forward (you can just press them down a bit, if needed).

Now go turn on the power switch or breaker for your HVAC unit… and sprint back to your ecobee3’s wall location. Mostly likely, you’ll be greeted by something awesome that looks like this:

ecobee3 start-up screen

ecobee3 start-up screen

If this is what you see, it’s time for that victorious arm thrust! BOOYAH!

If you see nothing, don’t worry — go back through and re-check all your connections. It’s possible a wire came loose, or maybe you accidentally swapped a couple of wires. There’s also a troubleshooting section in the installation guide, and you can always call ecobee’s tech support and they’ll help you out. I don’t get paid by ecobee, however, so posting install problems in the comments below won’t help you much. 🙂 I do, however, recommend you stop by the SmartHomeHub discussion forums and check out the ecobee3 Install Help thread for community-based help from other ecobee users.

Step 8: Initial Configuration

Once your ecobee3 fires up for the first time, it will auto-magically detect which wires are connected, and show you a screen like this to confirm:

The ecobee3 auto-configures based on which wiring terminals you connect

The ecobee3 auto-configures based on which wiring terminals you connect

If everything is correct, continue on with the rest of the ecobee3 setup wizard. It will walk you through configuring your equipment (and any accessories), setting your preferences, connecting the ecobee3 to your wireless network, and registering your ecobee3 so you can access it through ecobee’s web portal.

Step 9: Install Your Remote Sensor(s)

Resist the urge to tinker with your new ecobee3 just long enough to also install your remote sensor. Your ecobee3 comes with one remote sensor included, but if you purchased more, just follow these same steps to install them.

While standing in front of your thermostat (it senses your presence and will “wake up” if it was “asleep), pull the tab on the back of the remote sensor to connect its internal battery. The ecobee3 should detect the sensor within seconds:

Remote sensor pairing screen

Remote sensor pairing screen

Just follow the on-screen prompts to finish pairing, then place the remote sensor somewhere else in your house that you’d like to monitor. Check the ecobee3 installation guide for specific tips on where to locate it, but I recommend anywhere in the house where the temperature differs greatly from your thermostat location (my office, for example, is always a few degrees hotter in the summer, and cooler in the winter, than the kitchen where my ecobee3 is installed). Make sure the sensor is around 5 feet off the ground.

After your remote sensor is installed, I recommend enabling both the “Smart Home / Away” and “Follow Me” features of the ecobee3, as these will permit your smart thermostat to be as “smart” as it can. You can access these settings from the ecobee3’s “Sensors” menu.

Step 10: Install the Mobile App and Access the Web Interface

To truly get the most out of the ecobee3, I highly recommend installing the new ecobee3 smart phone app (available on iOS and Android), as well as spending some time in the web interface, accessible by logging in at The web interface also works great with iPads and other tablets.

Step 11: Join the ecobee Conversation at


Now that you’re “part of The Hive,” I invite you to come join the ecobee user discussions happening at It’s a user-driven discussion forum focused on all things home automation, with a lot of ecobee owners taking part. Though not an official ecobee company resource, you’ll also find that a number of prominent ecobee staffers hang out there, and they are always happy to hear user feedback and suggestions for tweaks, fixes, and new features.

As always, I welcome your comments and feedback below. But remember: as I mentioned earlier, I won’t be answering any ecobee3 tech support questions here. I’ll answer general questions, but for support I recommend contacting ecobee support directly, or asking your questions at for unofficial community-based support (where I do take part in the support conversations).

Welcome to The Hive!