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!

  • Pingback: ecobee 3 Review | Steve Jenkins' Blog()

  • What if my current thermostat has five wires and no common; R, G, Y , O, and Aux/E? Would I just bypass the W2/Aux wire around the PEK?

    • Hi, Eric. I’d call ecobee support to be sure, but my guess would be to do exactly that.

      • Actually I’m now thinking that would be wrong. When setting it up in that standard diagram, they combine the W and Y wires. In that setup W=heat, Y= cool. On a heat pump setup, however, the wiring is Y=cool, W/O/B = compressor, and W2/Aux= heat… so that would suggest that it is the compressor signal, the O wire, that I want to remain independent and join the Aux and Y wires in the PEK.

        • Hmm… I think you could be right! And shameless plug time… this is a perfection question to post over on As more people install these (and my gut says the ecobee3 is going to be popular), I’m sure there will be similar questions. We’d love to have you over there! 🙂

          • Thanks Steve… I will post.

            Yup, kicking myself that I just bought two SIs, a month before the 3 came out… can’t justify switching them out yet (particularly since I haven’t even installed one of them yet!)

  • I was hoping to see a discussion about how you connect to the house wireless net, and then how you connect the app of choice (in my case iPad, iPhone). That could then be followed by suggestions about whether running the full dialog thru the thermostat is good, or easier/harder to use an app.

    • Hi, Charles. That’s an easy one to answer. The setup wizard connects the ecobee3 to your WiFi network by simply scanning for it and allowing you to enter your WiFi password. Once connected, it spits out a 4 letter code.

      Next, just download the free mobile app, register a new account with your email address (you can also do this on their website, but it was super easy with the app) and then type in the 4 letter code to associate your thermostat (which is already connected to your WiFi) with your newly-created account.

      From that point, using the touch-screen interface is identical to the mobile app, with the exception of some setup menus on the wall unit (which you’ll probably never touch).

      The entire process takes maybe 5 minutes.

  • Eric Demers

    Hey Steve, what about an upgrade from the current ecobee Smart system? You have the 4 wires from the main unit to the controller (D-/D+,etc…). Do you need to push a new wire down? Is there an easy way to upgrade? Thanks!

    • hi, Eric. I’m actually working on an “upgrade” install how-to for original Smart owners right now!

      • Eric Demers

        That would of been good! I ended up just bypassing the old unit altogether, and hooking up the thermostat cable YWGRC connections directly to the furnance. Wish they had made it simpler, like hook up to the old control lines for the thermostat controls.

      • Stuart Winston

        Steve, have you finished this project as I’m trying to do this upgrade?

  • Steve–thanks for this. Like Eric, I’m interested in seeing how upgrading from an existing ecobee Smart Thermostat works. It sounds like the existing panel next to my furnace will need to be removed? Thanks!

    • Hey Mike, you are correct. The equipment interface module (EIM) is not needed and not compatible with the ecobee3 thermostat.

      • My HVAC pro installed a humidifier and dehumidifier (I don’t run them at the same time 🙂 ) to my existing Smart thermostat.

        Since the Control Panel is now to be removed, would I now have to wire the humidifier and dehumidifier all the way to the ecobee 3–which is located down the hallway and through a door in relation to the furnace? Or would they simply wire directly into the furnace?

        I’m game to get the 3 and try to install it, but I’m hesitant to if I have to run new wires through the walls/ceiling.


  • Paul Hansen


    I have the option of using the PEK or not on my ecobee3. I was thinking it might be possible to use that 5th wire to get the connection from my humidifier to the Ecobee if I used the PEK. Is this possible? Basically having the R G W Y connections connected to the Ecobee via the PEK would free up the 5th (blue in my case) C wire for me to use as a connector for the humidifier as long as I can still use the Rc connector as a return as you show in your other guide for the old smart thermostat.

    Thanks for your help!

    • Paul: I haven’t tested personally yet, but if you have five wires from your furnace to your wall location, you should be able to use the PEK, then use the 5th wire as the AUX+ for your humidifier, then wire the other side of the humidifier solenoid to the C terminal on your furnace board. Please let me know if that’s what you end up doing.

      • Paul Hansen


        I used the spare wire freed by using the PEK to connect to the ACC+ and wired it into the humidifier. I bridged the ACC- to the Rc terminal (like your old config) on the inside of the EcoBee3 panel to close the circuit. I’m not certain the humidifier is running though as I can’t tell if it kicks on or not but the fan runs when I do the humidifier test in the software for the Ecobee3. I have images here if you want to see. Is there any way that I can confirm that the humidifier is firing other than knowing that the fan kicks on when I test it? – Images

  • Pingback: Review: ecobee3 Smart WiFi Thermostat - Smart Thermostat Guide()

  • Seth Fiermonti

    My thermostats only have 2 wires – white and red. I have just baseboard heating ONLY – no AC. What should I do?!

  • Can this support zone systems with one unit or do I have to replace each of my thermostats with a separate one of these? I have two units, one with two zones and the other with a single zone.

    • Hi, Jawwig. The ecobee3 is designed to operate a single zone, and then its remote sensors are designed to optimize that single zone for comfort, based on where (and when) different parts of that zone are occupied.

  • Davoo

    It looks like the EcoBee 3 does not have dry contact terminals. What happened to your waterbug?

    • I moved it over so that it’s monitored by my DSC alarm system. 🙂

  • Lee Ragsdale

    Steve – building a new house and ordered two ecobee3 to install. My HVAC contractor (who would not order the ecobee3 himself) has said that the thermostat will not work until WiFi is active in the house, so I have a “non-smart” honeywell mounted on the wall now. Seems odd that WiFi is a mandatory requirement for install and configuration of the system. Is that the case, or are they just throwing up their hands without trying?

    I am certainly going to have WiFi and broadband after moving into the house. It just seems silly to have a plain thermostat installed when the smart thermostat is sitting right there.

  • Jalpa_Mike

    Steve, did you try the “Nest” controller? Just curious of your thoughts of Echobee versus Nest.

    • I’ve tinkered with the Nest, but haven’t lived with one. My overall thoughts are that I prefer the schedule-based approach (with smart occupancy) of the ecobee vs. the continually learning approach of the Nest.

  • Hiroshi F

    NOTE: Recent versions of the ecobee3 have a known manufacturing defect in the PEK, where the W/Y wires on the receiving hub do not match with the silk screen of the circuit board (W is heating, Y is cooling). This will cause your AC to turn on for heat and vice versa. Swap the wires if you have this issue. Picture for reference of what the defect looks like. Note the swapped W/Y.

    This page comes up near the top results for ecobee3 installation and I don’t have a blog. So dropped it here.

    • Hi, Hiroshi. I ran this by my contact at ecobee and got this in return:

      ecobee has been made aware of a manufacturing defect that involves a mislabelling of the Y and W terminals on the Power Extender Kit for the ecobee3. We’re still investigating, but believe the issue is impacting a very limited number of Power Extender Kits. The ecobee3 thermostat is not impacted and the issue does not apply to the Power Extender Kit for the Smart Si thermostat.

      The mislabeled Power Extender Kit would cause heating to turn on when cooling is expected, and vice versa. Customers who have a mislabeled Power Extender Kit would detect the issue during the installation process when they test that their heating and cooling equipment operates as expected. If a customer’s heating and cooling operates as expected, they are not impacted.

      Our early investigation points to the issue being caused by a small number of early Power Extender Kit terminal blocks being included in final production design. Once ecobee was made aware of the issue, it immediately worked with its manufacturing partners to remove defective Power Extender Kits from their inventory.

      ecobee apologizes to customers who have been impacted by the mislabelling and will replace Power Extender Kits that are defective. ecobee customer support is available to customers who have any questions or concerns at 1-877-932-6233 or [email protected].

  • Pingback: ecobee3 Review Followup: Two Month Update - Steve Jenkins' Blog()

  • Pulkit Dabral

    I moved into a house where AC was installed in 2004..I am trying to find the HVAC control board but am not really able to find it. Are they generally near the actual AC unit or more like a seperate board in the attic or someplace? I have a ranch style home.

    • Hi, Pulkit. It will be inside the furnace. You’ll have to remove a panel. Check the photos in my article and kill the power before you proceed.

      • Pulkit Dabral

        thks..sorry for the dumb question but by furnace you mean the actual AC unit placed outside the house?

        • HI, Pulkit. Not a dumb question. 🙂 The control board will be inside the large unit inside your house (probably in the basement, a utility room, or the garage). It’s also your furnace that heats your house in the winter. It will look like a large box with vent slits on the front and ducts connected to it. The AC unit outside is not what you want. 🙂

          • Pulkit Dabral

            thks Steve..I have a ranch style house…I do not see the furnace in either of your listed guess, it might be in the attic so will look there..

          • Yep – that’s the next place I’d check! 🙂

  • Pingback: Review: ecobee3 HomeKit-enabled Thermostat -

  • Nishawn

    I had the unused blue wire coming from the wall. I installed it in the C spot. However, when I went to the unit the to ensure the C wire was connect to the control board, I could not find the control board with the matching wires that were at the thermostat. There are a bunch of wires, but I don’t see the R-W-Y-G-B at a central point. I turned everything on to see what would happen. Every time the unit attempts to turn on, the ecobee shuts off and reboots and the unit itself never fully turns on.

  • Stallion V

    Hi Steve,
    Thanks for the detailed post its indeed very helpful.
    I am trying to replace our current non wifi version of Honeywell thermostat system with Ecobee

    We have a 3 level home and the Each level seems to have a control panel.
    The living area on Level 2 has a bigger panel as shown in picture 1 and Level 1 and Level 3 have their own panels as shown in picture 2.

    I am not sure whether I need to get 3 ecobees or just 1.
    If 1 and I install in the living area what happens to the other controllers.

    If you have any insights that would be much appreciated.

  • All I can think of is that the wires are connected wrong on the furnace terminal. Don’t trust the color of the wires put in by the original installer. Verify that the wiring at the furnace terminal is correct, and that the terminals on the ecobee connect to the right terminals on the furnace… regardless of the wire color.


      but all is fine with the previous thermostat which is now reconnected. nothing strange with wiring and color coding there.

      i fear having to crawl around in my phoenix attic to check out the furnace…it’s still 100+ here outside the home…may have to wait a few weeks.


  • Sounds like like the wires aren’t connected to the proper terminals. I’d go through and double (or triple) check. All the thermostat does is “close” connections to send signals to certain equipment (fan, furnace, A/C) to operate.

    • zionita

      Triple checked already.

  • Bob

    Is there a way to make the ecobee control a house ventilation valve, so that I can stop using a manual timer?

  • rafael fernandez

    just installed my ecobee and ran into the 4 wire issue. and because nothing can be easy in my house the air handler cable access had no C wire connection. After calling tech support they explained the B can work as a C. once i did this and hook it up to the PEK it started working just make sure whatever else is hooked up to the B besides the thermostat stays there (i.e. the compressor in my case)

  • Count_Iblis

    The PEK sends the power through the Rc wire then? I have a bad wire in my harness and the green fan wire isn’t connected. I’m guessing this won’t be an issue?

    • Yes, the power is through the Rh/Rc wire, so you SHOULD be OK. 🙂

  • Fidrych

    I am trying install the ecobee3. I have a heat pump and the thermostat has 7 wires. Rc, Y, B, O, G, W1 and X2 , I am not sure if I need all 7 to hook it up or if I cannot use some of them. I have attached an image of my current thermostat. Can you assist me in which wires I should hook up where?

    • Hi, Fidrych. Your best bet is to call ecobee Support. They can walk you through it over the phone way better than I can in comments.

  • I wire one side of the humidifier solenoid to the ACC+, and the other directly to the COM terminal on the furnace. Give that a shot, then make sure it’s set up properly . I talk a little more about my humidifier connection on this separate article:

  • Hi, John. Hard to say what the problem is. I’d try ecobee phone support or come post the issue at

  • If you have enough wires, you should wire individual wires from the W1 and W2 furnace terminals to the W1 and W2 terminals on the ecobee. W1 is for first stage heat, and W2 is for second stage heat. My guess is that your old thermostat wasn’t “smart” enough to choose which stage to fire, which is why the original installed jumped them like that. If you don’t have enough wires and can only choose one, run the W1 terminal on the ecobee to the W1 on the furnace, and forget about W2. But ideally, wire them both individually for the most efficient results!

  • Hi, Tom. Your best bet is to post the issue on I’m sure we can help you figure it out there. 🙂

  • Aaron Kraljev

    You sir are a magician. Got my EB six months ago but just now realized I did not hook her up right when the ac would not fire. This was key in helping me sort it out.

  • Yep! As long as it’s a legit and safe ground, that will work!

  • eevana

    I watched numerous videos and read counless articles on how to successfully install ecobee3 (without the c wire), and none of them made me feel comfortable about doing it until I came across this post. Thank you for taking the time to write this and doing such a good job! The most helpful part was where you explain that we may have extra wires, but to only meddle with the ones also attached to the thermostat. Thanks again!

    (I ended up frying the transformer because I didn’t trim all of the wires properly and two made contact, but according to tech support, I did a great job otherwise. 😀 Not bad for my first attempt at electrical, well, anything.)

    • I hope the transformer was easily replaced… but good job having the courage to do it yourself! 🙂

  • Awesome! 🙂

  • Woot!

  • Pingback: ecobee3 Does Everything Advertised, and More! - iOS Etc()

  • Cole

    How do you make this work if your furnace has a TV, W AND T TERMINAL (also has a TP and Z-which is connected to the W)?

  • John

    Here’s a problem I have after installing the thermostat, both the heat and A/C are running at the same time. Not sure what to do. I’ve cut the breaker off to the A/C and, of course, no A/C. I do have heat, which I need right now, but I’d like to have it setup right.

    • I’d check to see if maybe the wire insulation has rubbed through and your heat and cool wires are touching, which would energize both terminals whenever one is called for. But it’s definitely something wonky with the wiring.

  • TryingE3

    I have both Rc and Rh. My control panels are separated: AC has its own (old style water cooling AC, installed inside my home), while heating has its own panel. All wires eventually meet at the tstat (old Honeywell digital). So, tstat has 5 wires. See pics.
    Looks like I need the power extender – but since the 2 control panels are far apart, I would have to run new wires from one of the panels to the other in order to connect them all to the PEK.
    Is there an easier way?

  • Robert L. Harris

    Just got this link from a guy on the Facebook Smart Things User Group. 20 minutes later, after a pre-read, and PEX install I’m up and running. GREAT writeup, thanks.

  • Juan Carlos Martinez C. Steve, I have a european boiler that works with a 220VAC signal to the thermostat. In order to make ecobee work with this boiler I was planning to make an auxiliary panel below the boiler to feed the thermostat with a 24VAC signal as described by this drawing. Do you think it will work this way?

  • Pingback: ecobee3: Upgrading to a Smart Thermostat | everything emelia()

  • Chris Norman

    What are my options if I have only heating in my apartment and there is only 2 wires between the thermostat (it is the original one from when the place was built I think it has a little glass tube of mercury) and the much newer (probably installed in the 1990’s or so) furnace? The furnace has a place for a C wire on the board, just no additional wires between the the furnace and the thermostat?

    Also, is there a reason why it seems like none of the smart thermostat makers include any kind of external power supply for their thermostat’s? Seems like it would be much easier to plug it into a wall socket than to rewire the furnace!

  • Pingback: Ecobee Thermostats - Sdcma()