Why Does Ecobee Need A C Wire?

Do I need a C wire? Yes! You should ensure you install a C wire if you are upgrading your thermostat. Almost all modern thermostats, whether smart or not require a power source. This doesn’t seem likely to change anytime soon.

If you have Ecobee thermostat and only have two wires, a red and white one, with no C wire, then this is the article you have been waiting for.

What is C Wire?

Back then, thermostats used to be simple devices of on and off, and they didn’t need a continuous power supply. But the modern thermostats with backlit display and Wi-Fi, by contrast, require to have a steady supply of juice.

The C wire, or the common wire, then enables the continuous flow of volt power to the thermostat, usually 24 volts.

Technically, power usually flows from the red wire, but it is not continuously (not on its own). For it to be made continuous, it requires a common wire that will complete the circuit. When the circuit is complete, energy (24 volts) will flow continuously.

If you are considering buying a smart thermostat, or you already have one, then you’re probably thinking of installing it yourself. After all, if you can change a light switch or receptacle, then you’re skilled enough to install a smart thermostat.

If you have your system with a C wire, then it might just be tucked away behind your current thermostat, or it may be in use.

But if your system does not have a C wire, then you’ll need to run another new cable from your furnace to the thermostat to install most of the modern smart thermostat models.

What Should I do if I Don’t Have C Wire?

These are a few things that I would recommend you do if you don’t have C wire.
You can hire a pro who will run new wires between your furnace and the thermostat you have. (You may also do this yourself). Then grab a Venstar Add-a-Wire, that adds a 5th wire to the four wire setup you have.

You can also get a smart thermostat that’s designed to work with a system that lacks a C wire, like the ecobee3 (which has an adapter for C wireless system) or the Emerson Sensi (which doesn’t need a C wire in most systems).

Do I Need Common Wire (C Wire) for Nest?

Thermostat models like the Nest Learning Thermostat and the Honeywell Lyric can use the C wire, but they don’t need it. If your HVAC system may not be having a C wire, these thermostats and some others will draw power directly from the other wires when the heat or the AC is on.

This is power stealing, and it can work, and it did work well in the olden days though there are some inherent risks of using it.

What is The Work of A C Wire?

The C wire is a low voltage power wire that Wi-Fi thermostats need so that their advanced features can work properly. Most older homes may not have the C wire installed because the old thermostat models dint need one of them.

The old model thermostats were just simple devices, and dint needs a continuous power supply. But, the new smart thermostat models, have backlit displays and Wi-Fi connectivity that needs to have a steady stream of power.

Ecobee Solution

A little side story from this though. We didn’t realize that it was going to be this simple, so we bought four Ecobee thermostats from the home depot on a Saturday morning and later returned them the same Saturday night.

Because we had figured that we are just out of luck, but I was so determined that there must be a solution to this problem of not having a C wire to Ecobee thermostats in my home without having to spend an arm and a leg to have an electrician come in to rewire things. So I started to Google for hours and found all sorts of other problems but not this in particular.

I hope that this information here helps someone else out there before they make the mistake of returning their thermostats. If you are just starting out on this home automation journey, then you may also want to check out my article 11 tips for smart home beginners.

Best Customer Service For Smart Thermostat

I am completely amazed at the Ecobee customer service and also the quality of their product is very amazing. Sometimes you may get a defunct product, and if the company that manufactured it is more than willing to own up to the mistake and have good care for their customer like Ecobee, then they end up getting good reviews like this.

If you would like to have a look at the current prices of Ecobee thermostats, then you can check out here on Amazon.

All I am saying is that Ecobee makes one the few best thermostats. Maybe, maybe not but for my part, it was worth the money in my opinion to have such good customer support. That is very priceless!


If you are reading this post, then there is a high probability that you either have a Google Home or are probably looking for an Ecobee thermostat or two. I have been having some good luck with this on both the Google home and the Alexa platforms.

I would personally say that they are both equally the same as far as the setup time. From my experience with them, neither the Google Home Mini nor the Alexa has any real pitfalls when used with the Ecobee app except only one, humidity.

So this is it, you have it now. All you may need if you don’t have a C wire is a 24 volt AC adapter for each of your Ecobee thermostats, and you’re good to go. I’m no math guru, but this makes so much sense to me rather than calling an electrician. This will help you to install without a C wire. You can get the 24 Volt AC adapter here on Amazon.