The Best Wifi Thermostat Without a C-Wire

Nest Wifi Thermostat Without a C-Wire

So you’ve decided on dragging your old home into the 21st century with some home automation, congrats! It’s really exciting if you’re going the DIY route and installing your devices yourself.

Most projects are as simple as installing a light switch, but some can get more complicated.

One of the toughest projects is your thermostat, especially a wifi thermostat without a C-Wire, you… Wait, what’s a C-Wire? And what does it have to do with your smart thermostat? There’s a lot to learn about home automation for the DIY expert, but we're here to help you. Don’t worry, you’ll be installing your wifi thermostat in no time!

What is a C-Wire?

A C-Wire, also called a “common” wire, this is an electrical wire inside the wall that supplies continuous power to your thermostat. That way, your smart thermostat can communicate through wifi and keep an LED screen lit.

Basically, it needs a steady supply of 24V electrical power. The red wire (one of the colored wires you use to replace a switch or outlet) can supply this power, but not by itself. The device needs that common wire to complete the circuit and make that 24V power a continuous stream.

Do All Houses Have a C-Wire?

Unfortunately, no. A C-Wire isn’t as common as the name would suggest, as older model thermostats don’t necessarily need one.

If you do have a common wire, it can either be hooked up to the thermostat and furnace, or if unused, it can also be in the wall behind your current thermostat.

To see if you have one, you need to first open your thermostat and furnace and look to see if there is a wire connected to a terminal marked C. Usually, this common wire is blue or black, but be advised that many electricians are “creative” when it comes to using wire colors!

If you don’t see a wire connected to the C terminal, then you need to check the wires inside the wall to see if there is an unused wire in the bundle that could be your C-Wire.

No C-Wire? Don't Worry!

Another option if you don’t have an active common wire is to install your wifi thermostat without a C-Wire. I know I just made it sound like it needs one, but installing a smart thermostat without a common wire isn’t impossible!

Of course, you can buy spools of common wire to run from your furnace and AC to your thermostat, but that’s just a bit intimidating, right? Luckily, it’s not your only option. There’s a product that helps you install a smart thermostat without a C-Wire, and that’s the Venstar ACC0410 Add-A-Wire. This product is significantly easier to install than a line running through your whole house, of course.

Check out this install video, to see how easy it is:​

You can also find wifi thermostats that are designed to work without a common wire at all for a truly wireless device! Let’s compare a couple of these types of thermostats to see which one is best for a seamless smart home.

Two of the most popular smart thermostats that work without a C-Wire are the ecobee3 and the Emerson Sensi. Both are compatible with the Amazon Echo, making them a great addition to a whole smart home system.

Let’s look at how these two wifi thermostats stack up.

The Ecobee3

The ecobee3 is one of the most popular smart thermostats on the market today.

It has a lot of cool features like a touch screen display, a modern look to the console, moveable motion and temperature sensors for various rooms, usage reports, and of course connectivity via your smartphone.

To install the ecobee thermostat without a C-Wire, you’ll need a power extender kit. This is kind of like the Add-A-Wire, only built specifically for the ecobee3, and it can be kind of complicated to install. You may have to adjust wires in your furnace, which can be scary for some DIY homeowners. That being said, many homeowners have conquered this task, so installing this wifi thermostat without a C-Wire is possible!

The Emerson Sensi

The Emerson Sensi is also a very popular smart thermostat and it’s considerably cheaper than the ecobee, the Honeywell, or other smart thermostats.

The reason for this price break is that it comes with less features. It has the typical smart thermostat features like wifi connectivity and smartphone controls, but no usage reports or motion sensors.

It also has a more traditional thermostat look, which many seem to prefer. Basically, it’s a simplified, but cheaper wifi thermostat. Without a C-Wire, you can easily install it, too. You don’t even need a kit like the ecobee3! The Emerson Sensi is billed at being perfect for a DIY installation.

For this reason, we think the Emerson Sensi has the edge. If you want to create your smart home yourself, this wifi thermostat is best for a home without a common wire. You can easily get it set up and be on your way to a fully automated home in no time!

The Emerson Sensi

This thermostat requires a C-Wire if you are hooking up only heat or only cool.

If you are hooking up both heating and cooling, it does not need a C-Wire.


There are quite a few wifi thermostats without a C-Wire out there, however, not all of them are up to snuff or they're sold at a premium. If you're in the market for one, I highly suggest the ecobee3 and the Sensi mentioned above.

Alternatively, if you have a Z-Wave home automation system, you can get a Z-Wave thermostat which would likely integrate with your system better anyway.

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