Smart Thermostat Without C Wire [How to install it]

Imagine buying a new smart thermostat, patiently waiting for that Amazon box to be delivered. You open it up, read the instructions, maybe watch a video that tells you how to install the device.

You remove your existing thermostat to find that things aren’t quite right – you don’t have a C-wire. A C-wire or common wire is a power supply required for your smart thermostat to work correctly.

You can learn more about the C-wire and why it’s important in our article here. Unfortunately, most of the older thermostat models didn’t require one, so many homes do not have a C-wire installed.

Almost all Wi-Fi thermostat no c wire models require a common wire. But, just because you don’t have one does not mean you will never be able to get a smart thermostat.

Many buyers wonder if they can install a smart thermostat without a C wire. There are several ways to install programmable or Wi-Fi thermostats without a C-wire; it takes some additional work. We’ll walk you through your options below.

How to Install a Smart Thermostat Without A C-Wire

The first thing you want to do is check for a C-wire by looking at your old thermostat.

  1. Detach your thermostat and take a look at the wires connected to it
  2. If there is a terminal labeled “C,” then you have a C-wire
  3. If there is not, go to your furnace and check the source

Sometimes your furnace has a common wire that wasn’t needed during installing your existing thermostat so that the wire can sometimes be hidden in the wall. If there is no C-wire on your furnace, then take a look at these simple workarounds that will teach you how to install a smart thermostat without c wire.

Get a Wi-Fi Thermostat that Works Without A C-Wire

The simplest solution would be getting a smart thermostat that doesn’t require a common wire to work. The following thermostats work without a c-wire.

Ecobee4 and other Ecobee Thermostats

The Ecobee4 is our pick for the best thermostat with remote sensors. Ecobee smart thermostat without c wire comes with a “power extender kit” to replace the C-wire.

This Ecobee power extender kit will work with Ecobee4, Ecobee 3, and Ecobee 3 Lite thermostats. Installing the power extender kit is very simple and took us about 10 minutes during our testing.

All you must do is connect your existing wires for your furnace into the power extender kit and then wire the extender to your furnace. Ecobee has a great video below that shows how easy this is to achieve.



Check out our review for more information about the Ecobee4 thermostat with remote sensors.

Google Nest Learning Thermostat

The Nest Learning Thermostat is our pick for the best smart thermostat. In most cases, a Nest Thermostat no c wire can work without a common wire. Without a common wire, it charges its internal battery using power from the heating and cooling wires.

Some HVAC systems, such as micro-controller-based systems and certain gas valves, will require a C-wire to work with Nest Learning Thermostat. You can read more about Nest thermostat’s C-wire compatibility on their website.

For more information, check out our in-depth review of the Nest 3rd Generation Learning Thermostat.

Lux Geo thermostat without a common wire

We reviewed some lesser-known models in our guide to the best wifi and programmable thermostats.

A critical model to take note of is the Lux Geo Smart Thermostat. Lux Geo is very likely to work with your system when nothing else does. It is affordable and can run on AA batteries.

With batteries installed, it does not require a C-wire or any adapters to power the thermostat. Also, it can work with two-wire systems, which are incompatible with any form of a C-wire replacement.

If you want to get a thermostat that is not mentioned above and requires a C-wire, you should consider hiring a professional who can run a C-wire from your furnace to your thermostat.

It’s possible to do this work yourself, but home electrical work is not for the faint of heart. If you have never done something like this, it is best to leave it to someone who has.

A quick visit to Amazon’s Home Services center makes it easy to find someone to install the thermostat for you, including your new common wire.

Venstar Add-a-Wire Adapter

If running a common wire is out of the question, and you’re installing a smart thermostat that’s not listed above, you have one other option for installation.

The Venstar Add-a-Wire is a DIY-friendly alternative that allows you to add additional wiring in systems where new wiring can’t be run. This accessory is effortless to install, and it is much easier (and cheaper) than running a completely new wire.

Adding this adapter is not that difficult, even if you are not experienced. The installation for our test took less than an hour. Most of the work is in twisting wires and matching colors—the included instructions for the adapter to make things easy.

Here is what you’ll need to install a Venstar Add-a-Wire adapter:

  • Screwdrivers
  • Electrical tape
  • Two-wire nuts (included)
  • Needle nose pliers
  • Access to furnace and thermostat wiring

Venstar put together a short video to show how easy it is to install the unit.

Keep in mind that your furnace panel will likely be different from the one shown in the video, but the process remains the same.

Substitute a G-Wire for a C-Wire

A C-wire provides constant power using the furnace as a power source. The G-Wire connects to the fan, and you can easily substitute it for the C-wire.

This solution works the best if you have a forced-air, gas, or propane heating and cooling system. While it’s a decent substitute as a power source, this method will remove the ability to control your fan.

The fan will run when your system does, so the trade-off is you lose some functionality compared to your current HVAC configuration.

To see how to substitute the G-wire for the C-wire, check out this two-minute overview on how to do it.


Add a Transformer

Thinking about adding an external transformer may have you running for the hills. Wiring an external device into your system will allow you to get a Wi-Fi thermostat that needs a C-wire to work correctly.

We think installing a transformer is probably the most overkill of all your options so that we won’t go into much detail here. But for some people, it may be their only option.

For more information, check out this guide over at The Balance.

Wi-Fi thermostat no c wire: Conclusion

Keep in mind that, unless stated otherwise, the Wi-Fi thermostat you want to get requires a C-wire.

It is highly recommended to check your HVAC system and see if you have a C-wire before buying a new thermostat. If you don’t have it, then pick one of our solutions that will work the best for you.

Even if you are a newbie to installations, don’t panic. It is not as complicated as it seems, and the step-by-step video instructions we included are straightforward, and anyone can follow them.

Smart Thermostat Without C Wire: Amazon Best Sellers

Save 7%Bestseller 1
Cielo Smart Thermostat | Supports Conventional Systems up to (2H/2C) & Heat Pumps (4H/2C) | Alexa, Google, Siri Shortcuts, SmartThings, IFTTT | Touchscreen Color Display | Free C-Wire Adapter
57 Reviews
Cielo Smart Thermostat | Supports Conventional Systems up to (2H/2C) & Heat Pumps (4H/2C) | Alexa, Google, Siri Shortcuts, SmartThings, IFTTT | Touchscreen Color Display | Free C-Wire Adapter
  • Smart Choice for Savings - Huge saving on your heating and cooling costs.
  • Elevate Home Comfort - Next-Gen features ensure your cooling or heating only runs when you need it, keeping your energy bills in check without compromising on comfort.
  • Intelligent Schedules - ensure a perfect home climate always.
Bestseller 2
MoesGo Programmable WiFi Smart Thermostat for Home, No C-Wire Required by C-Wire Adapter, with Zone Remote Sensor, Remote Control Tuya/Smart Life, Compatible with Alexa and Google Assistant, 24VAC
  • 【Wide compatibility with C-wire adapter/Not supported 2 wire】Suitable for Conventional (2H/2C); Heat Pump (4H/2C); Not support heating only systems(No C-wire)/high voltage systems(120V-240V)
  • 【Saving energy】Saving over 23% energy and create a comfortable environment.
  • 【Free Temperature Sensor】Free temperature sensor, for your better experience.
Bestseller 3
Amazon Smart Thermostat – Save money and energy - Works with Alexa and Ring - C-wire required
  • Smart upgrade - Amazon Smart Thermostat is an easy way to switch from a traditional thermostat and help reduce energy usage.
  • Save money - After purchase, Amazon will send you an email with details about rebates that may be available from energy providers in your area. Explore rebates above.
  • Save energy - According to EPA estimates, ENERGY STAR certified thermostats save an average of $50 on yearly energy bills.
Save 42%Bestseller 4
Honeywell Home RTH6580WF Wi-Fi 7-Day Programmable Thermostat
  • ENERGY STAR certified. Help save energy, track your heating and cooling with monthly energy reports and get personalized tips on reducing energy use.
  • SAVE ENERGY AND GET REWARDED by checking with your energy provider about available energy savings rebates to save on your purchase (rebate finder link above). Plus, eligible customers can enroll in...
  • C-WIRE POWER ADAPTER REQUIRED: Before purchasing, check to see if this thermostat is compatible with your home and to determine if your home needs a C-wire power adapter.
Bestseller 5
vine Thermostat for Home with Touchscreen Color Display, WiFi Smart Thermostat Compatible with Alexa and Google Assistant, 7day/8period Programmable, Energy Saving, C-Wire Required, Screen Size 2.8"
  • 【Wide Compatibility】This ac thermostats for home is compatible with 90% of system: Conventional (2H/2C); Heat Pump (4H/2C); Supports natural gas, electric, hot water, gas fireplaces (24 Volts),...
  • 【Quick Install】Our home thermostat for ac and heating can be installed easily in 20 minutes or less with step-by-step online guides and videos
  • 【Remotely Control & Voice Control】Control and monitor the wifi thermostat from anywhere using Vine Thermostat App or Smart Life App; Compatible with Alexa and Google Home for hands-free voice...

As an Amazon Associate I earn from qualifying purchases. Last update on 2023-12-21 from Amazon / Images from Amazon Product Advertising API

  • Updated October 29, 2021
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