Best smart thermostats that don't require a C wire 2024

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Many of the best smart thermostats require a C wire ("common" wire) to provide enough power for LED displays and Wi-Fi-powered advanced functions. However, many older homes' electrical systems don't have a common wire, and that's why some homeowners need smart thermostats without a C wire requirement. 

The thermostats below run on low power or ship with DIY power adapters that anyone can install. Here are our favorite picks that'll help you avoid hiring a professional to rewire your home — just keep in mind that some thermostats may come with the adapter, allowing you to install the device right out of the box, and with some, you'll need to purchase that adapter separately. 

Photo of Michael Hicks, Senior Editor of Android Central
Michael Hicks

Michael Hicks is Android Central's resident smartwatch geek, having reviewed or tested dozens of wearables from Samsung, Google, Apple, Garmin, Fitbit, Coros, Polar, Withings, Amazfit, and others. He spends his free time running or hiking while wearing several watches at once, testing which is most accurate.

At a glance

Best overall

Ecobee3 Lite

(Image credit: Ecobee)

1. ecobee3 Lite Smart Thermostat

Best overall

Specifications

Dimensions: 4x4x.8-inches
Display: 3.5 in. full-color LCD
Touchscreen: Yes
Program options: 7 Day Programmable, Geofencing or Non-Programmable
Performance features: Humidity Control, AC Protection, Smart Alerts, Circulating Fan, Two-stage heating and cooling, Pause when open
C-Wire adapter included: Yes

Reasons to buy

+
Lots of great smart features
+
Sleek, modern look
+
Great price point
+
Works with ecobee's smart security system

Reasons to avoid

-
No occupancy sensors
-
Only works with 2.4GHz Wi-Fi
-
The display is a bit cramped

When many people think of the best smart thermostats, two brand names tend to come to mind — ecobee and Nest. Ecobee takes the top spot on this list with its ecobee3 Lite Smart Thermostat thanks to not only the intelligence it can add to your HVAC system but also its affordable price tag and inclusion of a Power Extender Kit to work with homes that don't have a C-wire.

This smart thermostat employs all the research that ecobee has learned over the years to offer you a fantastic way to manage the climate in your home from anywhere you are. The ecobee3 Lite offers a way to easily set a program for every day of the week and break it down into different times. It can also recognize when you aren't home using your phone's GPS to reduce energy usage during those times.

There aren't many downsides to this thermostat, given the price range. But comparing it to the more expensive models in the lineup, it is missing occupancy sensors, only works on 2.4GHz Wi-Fi, and the display feels a bit dated in comparison. But, if you don't need a lot of gadgets in your thermostat and are on a budget, this is a great option for your home.

Best budget

Sensi Lite Smart Thermostat

(Image credit: Best Buy)

2. Sensi Lite Smart Thermostat

Best budget

Specifications

Dimensions: 5.07x3.13x.88-inches
Display: 2.3 in. full-color LCD
Touchscreen: Yes
Program options: 7 Day Programmable, Geofencing or Non-Programmable
Performance features: Flexible Scheduling. Filter Change Reminder, Monthly Usage Reports, HVAC Smart Alerts, Sensi Mobile App
C-Wire adapter included: No

Reasons to buy

+
Easy-to-read display
+
No C-wire needed for most systems
+
Works with many smart home platforms
+
Very affordable

Reasons to avoid

-
Design is boring for some
-
Software can be a bit buggy
-
No occupancy sensor

While it lacks some of the fancier features in the Sensi Touch Smart Thermostat, this Wi-Fi smart thermostat makes up for it with a budget-friendly price and ease of use. It has a simple and clear display with the temperature taking center stage. You can change basic settings on the unit itself, but the best way to control it is with the app.

A C-wire is optional but required for some configurations, such as a heat-only system. For most conventional HVAC systems, it's unneeded, and the unit has two AA batteries for power. This lets the thermostat stay powered up to manage your HVAC but also to allow for control when you aren't home.

The design of the unit will be good for some but seem bland for others. The Sensi Lite also lacks some of the sensors of other units, like occupancy. But the app will allow it to know if you are home or not with GPS. As for the app, it can be a bit buggy when making changes to schedules, but overall, it is a low-cost way to manage your HVAC.

Premium choice

ecobee Smart Thermostat Premium

(Image credit: Chris Wedel/Android Central)
Premium choice

Specifications

Dimensions: 4.09x4.09x1.02-inches
Display: 4 in. full-color LCD, 540 x 540
Touchscreen: Yes
Program options: 7 Day Programmable, Geofencing or Non-Programmable
Performance features: Humidity Control, AC Protection, Smart Alerts, Circulating Fan, Two-stage heating and cooling, Air Quality Monitor, Occupancy Radar, Proximity Radar, Pause when open
C-Wire adapter included: Yes

Reasons to buy

+
Large display wrapped in titanium
+
Air quality monitor built-in
+
Comes with a room sensor
+
Radar occupancy sensor

Reasons to avoid

-
Pricey
-
Can't be a Google Assistant speaker

ecobee's latest smart thermostat builds upon everything that made its predecessors great — it supports up to 32 room sensors, making it perfect for homes with multiple zones. In his review, Chris Wedel really enjoyed the beautiful display wrapped in titanium and the compatibility with most smart assistants.

The updated thermostat adds built-in Alexa and Siri voice controls with impressive built-in mics and a speaker, so you can easily change the temperature with a few words. It can even act as an excellent smart speaker — but not for Google Assistant. You'll also get a built-in air quality sensor to help ensure you breathe clean air.

The included Power Extender Kit lets you install this in homes without the C-wire, so you won't need to make any extra purchases to get up and going. While it is on the expensive side, this thermostat is nearly everything you could ask for. It will even display a video feed from ecobee's security cameras and even the ecobee Smart Doorbell Camera.

Best for Google

Nest Learning Thermostat

(Image credit: Android Central)

4. Google Nest Learning Thermostat

Best for Google

Specifications

Dimensions: 3.3x3.3x1.21-inches
Display: 2 in. full-color LCD, 480 x480
Touchscreen: No
Program options: 7 Day Programmable, Automatic learning schedule, Geofencing or Non-Programmable
Performance features: Flexible Scheduling, Filter Change Reminder, Monthly Usage Reports, HVAC Smart Alerts
C-Wire adapter included: No

Reasons to buy

+
Standout design
+
Great a learning your patterns
+
Nest renew feature helps you understand your energy usage
+
Easily configurable

Reasons to avoid

-
C-wire adapter is a separate purchase
-
Physically using the thermostat has a learning curve

The Nest Learning Thermostat remains one of the smartest and most useful thermostats today, supporting multiple zones, learned schedules, Alexa/Google Assistant integration, and HVAC monitoring. Oh, and it has a built-in sensor to know if you are home or not to do a better job of only running the system when people are home.

The unique, circular design with seven different finishes looks great, but learning the different twists, turns, and presses to control it can take some getting used to. Thankfully, the app is simple to use, which ties into Nest Renew to help show you how your home's HVAC affects both your energy usage and the environment as a whole.

However, you may encounter power cycling issues if you install this without a C Wire. Google sells a Nest Power Connector as a C Wire substitute for consistent power, but it won't work for every home. All Nest Thermostats are good enough to risk testing without a C wire, but keep the receipt just in case.

Best for window units

Sensibo Air

(Image credit: Sensibo)

5. Sensibo Air

Best for window units

Specifications

Dimensions: 2.56x2.56x.67-inches
Display: No
Touchscreen: No
Program options: 7-day schedules & Timers, Climate React, Geo-fencing
Performance features: Full control of AC from anywhere (including all modes, fan levels, swing, LED light, etc.)
C-Wire adapter included: No

Reasons to buy

+
Simple setup
+
Works with most window AC units
+
Offers good insight into your energy usage

Reasons to avoid

-
Some compatibility issues
-
Need one for each unit you want to control

C wire aside, some of you may not even have central air but will still want to manage the climate throughout your home. For that, the Sensibo Air controls your window or mobile AC appliances, letting you set up conditioning or heating schedules or pick specific temperatures through Wi-Fi monitoring. Plus, it makes your AC units controllable through Echo or Google Home commands.

There is no installation needed for this device, as it only needs to be plugged in, connected to your home's Wi-Fi, and have a line of sight to the AC or heater you want to control. This is because it uses IR, like the remote that came with your unit.

The app provides insight into your energy usage, lets you control the device from anywhere, and sets schedules as well. However, sometimes there are issues with compatibility where your AC may be set to Fahrenheit, but the Sensibo Air will continue to control it in Celsius. It's not a huge deal, but something to be aware of.

Best Google value

Nest Thermostat

(Image credit: Android Central)
Best Google value

Specifications

Dimensions: 3.3x3.3x1.07-inches
Display: 2 in. full-color LCD, 480 x480
Touchscreen: No
Program options: 7 Day Programmable, Geofencing or Non-Programmable
Performance features: Filter Change Reminder, Monthly Usage Reports, HVAC Smart Alerts
C-Wire adapter included: No

Reasons to buy

+
Low-profile, clean design
+
Simple controls
+
Easy-to-use app

Reasons to avoid

-
Doesn't work well with multi-zone setups
-
No sensor support

The newest Nest is another thermostat that can work without a C wire, but in our Nest Thermostat review, we ended up having to wire one in. If your HVAC is fully compatible, installation is relatively easy. Otherwise, try you'll need to purchase the Nest Power Connector to get things up and running.

It's a great-looking thermostat that comes with four color options, so it can look great no matter your home's style. Overall, it is a versatile and affordable machine that uses geofencing and motion tracking to detect when you're not home, saving you plenty of money.

It does lack the ability to work with room sensors like the Nest Learning Thermostat above, so no multi-zone support. The Nest Thermostat is also missing the learning part of its more expensive counterpart. But, you still get Nest Renew support and plenty of smart features to upgrade your home's HVAC.

How to choose

No C wire? No problem (mostly)!

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The majority of older homes and heating/cooling systems won't have a C wire. Since you may not be comfortable installing the wire yourself or paying for an electrician, these smart thermostats without a C wire will still reduce your energy bills. Some use batteries that you'll have to keep replacing, while others require a power extension kit that will still necessitate some simple wiring on your part. Many of these are among the best smart thermostats, so you can rest assured that a C-wire requirement doesn't equate to better quality.

Nest Thermostats may work in some homes without a C-Wire but there's still a chance you'll need some more power. Google has released the new Google Nest Power Connector to bypass the C Wire requirement, and it solved those issues for some people, but other reviewers report that their low power issues didn't go away even with the new Power Connector. So whether a Nest works without a C Wire may vary from one house to the next.

Whether your Nest or Nest Learning Thermostat will work with a Power Connector varies from home to home. For more consistency, consider ecobee instead.

If you have a little electrical know-how (and a little extra cash), the ecobee3 Lite Smart Thermostat will require you to wire in a power extension kit to replace the missing C wire. Thankfully, ecobee designed them with DIY installation in mind, so the process shouldn't be too complicated. Once installed, it's the best smart thermostat for multiple zones, meaning it's great for people with large homes where rooms are unevenly heated. From its multiroom sensor integration to its smart home integration to control your entire home, ecobee's offering is truly the king of smart thermostats — and its price reflects it.

Or, if you're feeling bold, you can take the plunge and use a simple Venstar kit to install a new set of HVAC-compatible wires. With this tool installed, virtually any of the excellent smart thermostats available should be compatible with your home's heating and cooling.

Michael L Hicks
Senior Editor, Wearables & AR/VR

Michael is Android Central's resident expert on wearables and fitness. Before joining Android Central, he freelanced for years at Techradar, Wareable, Windows Central, and Digital Trends. Channeling his love of running, he established himself as an expert on fitness watches, testing and reviewing models from Garmin, Fitbit, Samsung, Apple, COROS, Polar, Amazfit, Suunto, and more.

With contributions from