1. At a glance
2. Best overall
3. Best budget
4. Premium choice
5. Best for Google
6. Best for window units
7. Best Google value
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.
At a glance
Best overall
The ecobee3 Lite smart thermostat offers the features you'd want, like learning your climate preferences, integrating with your smart assistant, notifying you of potential HVAC issues, and more. It ships with a C-wire adapter and is at a great price, which is why it is at the top of our list.
Best budget
Not only is the Sensi Lite Smart Thermostat a great way to add some intelligence to your HVAC system, but it also comes with a low price tag and an easy-to-use interface. The device itself keeps much of the look of traditional thermostats but brings smart features to help save you money.
Premium choice
Here is the high-end model from ecobee that brings the best of what the company can offer into a single device. Wrapped in titanium, this thermostat monitors your home's air quality, acts as a smart speaker, a security hub, and much more. Oh, and it's great at controlling your HVAC.
Best for Google
Google made a big splash with the first Nest Thermostat, and it has continued to be a fantastic choice. With seven colors to choose from, this modern-looking thermostat learns your preferences and adapts to them while tying in perfectly with your Google smart home ecosystem.
Best for window units
Smart thermostats are great but don't work with window AC units. This device works with any AC or heater with an infrared remote and will give you control over your climate from anywhere you have internet. Plus, it offers smart features to help save you money while monitoring your energy usage.
Best Google value
The Nest Thermostat is a lower-cost option from Google that keeps much of what the pricier version offers but forgoes things like the presence sensor and metallic finish. However, it still has the smarts and a more subdued design.
Best overall
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
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 keep 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'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 that we reviewed.
Best for Google
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
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
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.
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.
