Heating & Cooling

Ecobee3 Lite Wiring Diagram (Complete Guide)

Ecobee Thermostat Lg

When you initially join the ecobee family, a few things become very important. These things range from keeping your bills down while utilizing HVAC appliances or simply becoming more in control of the constant temperatures in your home. 

You gain many benefits from the second your ecobee product walks through your door.

An ecobee3 Lite does not need a C-wire to have it installed. However, it will require a Power Extension Kit, which is the best solution for you right out of the box. This kit allows you to install the device directly on the furnace. 

That being said, the adage “Rome wasn’t built in a day” is true in more ways than one when it comes to ecobee3 Lite; there are several positive features to getting one. 

However, there are a few cons too, and one of the most glaring ones being the need to wire your systems if it doesn’t integrate fully out of the box.

What is a C-Wire?

Before we get to anything else, we should define what a C-wire is. A C-wire is also known as a standard wire, and its primary use is to carry continuous power to your thermostat itself through your house.

As we noted above, if builders built your house within the last decade or so, you probably have C-wires readily available behind your thermostat plating. Still, if not, there are options and solutions available.

How to Tell if You Have a C-Wire

The reference here is the potential lack of a C-wire in your systems, which would mean you need to do a few hands-on works to get the most out of your ecobee Lite. In doing so, you will be altering a few things with the Power Extender Kit.

Assuming your heating and cooling system is not the newest on the market or that your home is rather old, you may not have a C-wire in your setup. 

Unfortunately, not having a c-wire attached to your system means it may not make the most use out of your new ecobee 3 Lite without a little fine-tuning. 

Still, you can most definitely change this; how easy or difficult the process is depends entirely on how old we are talking.

Ecobee Wiring Lg

How to Locate Your C-Wire

One of the most significant ways you can tell at a glance would come from identifying whether or not you have a low voltage heating system. 

These low voltage heating systems typically run on a 24v, and when one gets installed, you will have a c-wire, also known as a “common wire.”

The best way to find the C-wire would be to remove the front cover from your current thermostat. In doing so, you will reveal a bundle of five different wires. 

Still, the one you are looking for is typically blue or black and will link directly to something labeled “Terminal C.”

There is the distinct possibility that you pop the faceplate off and notice less than five wires. It also may seem more concerning that there is seemingly nothing plugged into the C terminal at all. 

The wire itself may not be directly visible at first glance, but that does not necessarily mean it is not there. These wires have been known to get tucked into the wall after all.

Next up may cause concern for those who are not the most experienced or confident. You would need to pull the bundle of wires out a bit to check behind them to see whether or not the precious C-wire is located behind them. 

Suppose you have done all of the above and do not see the blue wire of truth. In that case, you may undoubtedly be down on your luck. 

Still, you are not entirely out of options. The Power Extender Kit included with your purchase can provide the solution you are looking for. 

Also, you should install the kit in itself inside your furnace instead of the thermostat. 

While it sounds more daunting, the process is not too different, but we will go more into that later.

Does ecobee3 Need C-Wire?

While you can install the ecobee3 Lite in homes with no active C-wire, the process is more complicated than usual if you had one available.

Thanks to the Power Extender Kit, you have a solution available to you out of the box. 

As we said above, you will install the kit itself directly onto your furnace. Despite the extra installation steps, it has the same functionality as placed onto the thermostat.

Another scenario you might find yourself facing is that you not only lack a C-wire, but you have two relatively thick wires. 

This is one of the worst instances you can be in because you more than likely have a “Line Voltage system.”

Sadly enough, there are not many intelligent thermostats compatible with it in the first place. That is unless they are explicitly made for it in the first place, ruling the ecobee3 out of the equation.

What to Do if You Don’t Have a C-Wire

Lacking a C-wire doesn’t mean the end of your journey to getting an ecobee3 in your home. 

Still, it does mean you will have to either get creative or expensive, depending on what solution you will go with. Below we will have two alternatives for you to decide on.

Option 1: Laying New Lines

If you lack a C-wire, there is one of the most considerable radical solutions out there. You could run one yourself by pulling out the existing thermostat wires that go from your furnace to your thermostat running new ones.

Laying new lines is not an easy job. Many people would quickly find themselves out of their depth going this route. 

In that case, if you genuinely wanted to get an ecobee3 Lite in your home, this is the most expensive but also a fail-proof option. 

Still, it would be wise to consider hiring a professional if you don’t have a background in electrical work.

Option 2: Utilizing the Power Extender Kit

The easiest option to go with, but available to people who lack the critical C-wire, is having four wires behind their thermostat plate. The PEK is used to install their system. 

The first thing you are going to do is turn off the power to all of your HVAC equipment for safety and take a picture of the wiring on your furnace control board and the wiring layout inside your thermostat for personal reference.

Next, you will locate the four primary thermostat wires on your furnace control board. The cables will be Red, Green, Yellow, and White. 

Still, there is the remote chance they have been spliced further but fear not, for they will ultimately lead back to the control board itself.

You will want to remove the wires from their current location and plug them into each of the color-coordinated panels on the PEK. 

You must line them up correctly to ensure you know how to install them to the ecobee3 Lite.

After you’ve gotten all of your colors connected to the PEK, you will want to close the panel located on your furnace and return to the Ecobee to get it connected. 

The setup itself is as follows:

R Wire connects to the RC terminal

G Wire connects to the C terminal

Y Wire connects to the PEK terminal

W wire connects to the W1 terminal

Assuming you’ve followed all the steps above to the letter, you can turn the power of your HVAC system back online. Then, take solace in the hard work you’ve done to get your ecobee3 online and ready to be used. 

If you are still having trouble, you can also utilize this instructional video above.

What is RC and RH on ecobee?

On the off-hand chance, you do have to dive into your thermostat’s wiring and make use of your PEK; you may be wondering what these labels mean. Luckily enough, we have just the answer to all those questions and more!

The Rc and Rh wires are both two sides of the same coin, being interchangeable with one another, meaning if you don’t have one, you will more than likely have the other. Still, they both serve the same purpose and are essentially R wires by default.

The first of the two, the RC, is known as the cooling power wire, and you will find it resting comfortably in dual-transformer systems. 

When you break this down, it means that you’ll traditionally have two R wires that each have different purposes. One governs heating, and the other regulates cooling, hence Rc and Rh.

One of the R wires will form the first part of the dual-transformer system, leading to the cooling transformer. If you can read between the lines, you probably guessed that the second R wire leads to the heating transformer.

Does ecobee3 Lite Come with a Wall Plate?

The ecobee3 Lite most certainly does come with a wall place. The optional plate is included to cover any paint discrepancies or damages that might have occurred throughout your initial installation. 

The plate in itself looks very sleek, and the dual functionality of covering up any blemishes makes it a nice little bonus for how cheap the overall product is.

How Do I Pair My ecobee3 Lite?

As with almost any technological device released nowadays, you will need to make sure both your phone and the Ecobee app itself are up to date. It also needs to be connected to the same Wi-Fi connection to sync perfectly.

If it is not working correctly, you may want to ensure that they are both connected to the same connection. 

Suppose you happen to have a dual-band connection. In that case, you’ll want to make doubly sure you are attempting to sync your devices through the 2.4 GHz connection and not anything higher.

Apple Devices

You would want to add an accessory on apple and go from there. Still, suppose you don’t have any other devices of similar nature. 

In that case, you will want to resort to the tried and true method of searching for nearby devices by clicking on the “Can’t scan or don’t have code” option.

After that, you are more or less home free. You get the code, scam it with your home app, and just like that, you are now paired up.

iOS Devices 

The two systems share a similar pairing process, but iOS is just a tad quicker. Download the ecobee app on your phone, ensure that it is up to date, as is your phone, and tap the account option located in the bottom right-hand corner of your screen.

Next, you will want to select “HomeKit” under the integrations menu and tap the “+” sign to search for new devices and add your thermostat. 

After this, you want to pick your home, add your ecobee, and finally test the connection between the two by hitting the “Say hi” option.

If you get the prompt saying “Hi there” on your ecobee, then congratulations, the two communicate correctly. 

All that’s left to do now is scan the code with the ecobee app, pick the room you want, and name it if you’d like, and your new thermostat is fully paired to HomeKit.

How Do I Know if My ecobee is HomeKit Enabled?

To tell whether or not it is enabled, all you need to do is search diligently on the box your ecobee3 Lite arrived in for the Apple HomeKit logo. 

If you’ve long since thrown the packaging in the trash, you can also look up the part number on the back of your ecobee3 to see if it’s enabled that way.

Advantages & Disadvantages of an ecobee3 Lite

As expected, the ecobee3 is not a perfect product, meaning it isn’t without its flaws. As such, here are some of the better and worse parts of this little thermostat.

HomeIQ shows data usage (once a month reading.)As stated, you can only get HomeIQ once a month, so delayed readings.
The touch screen display is very nice.The screen in itself is sleek but very prone to dirt and grime build-up.
It comes with an innate three-year warranty out of the box.Utilizing the PEK can be difficult if you do not know electric work.
Easy to read system alerts for keeping things the way you like them temperature-wise.Unless cleverly placed, intelligent sensors can hinder more than help despite the name.
Can work with or without C-wire (depending on circumstance.)

Final Word

The ecobee3 Lite is an excellent product in itself. While the wiring can be problematic if your home is older, they aren’t usually so complicated you can’t overcome them. 

You would want to check whether you are on a line voltage system for easy compatibility, though.



Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.