Our top-choice smart thermostats that don't require a C wire in 2021 are...
Many of the best smart thermostats require a C wire ("common" wire) for power due to their LED displays and Wi-Fi-powered advanced functions, leading homeowners with older heating systems to look for smart thermostats without a C wire requirement. If you don't already have a C wire in your system, these smart thermostats use separate power sources or adapters that let you monitor your home climate without having to hire a professional to rewire your home.
Simple and straightforwardNest Thermostat E smart thermostatStaff Pick
Our top pick for the best smart thermostat without a C wire goes to the Nest Thermostat E. Its display simply shows the temperature setting, while the app lets you prioritize certain rooms' cooling, change settings when you're away, and lets you know if it senses a problem. Most importantly, the Thermostat E features a built-in rechargeable lithium-ion battery that bypasses the C Wire requirement. So if you can still find it in stock, this minimalist thermostat remains a reliable, affordable option.
$137 at Walmart $119 at Verizon
Some rewiring requiredecobee SmartThermostat (5th Gen)
ecobee's 5th-gen smart thermostat builds upon everything that made its predecessors great - it supports up to 32 room sensors, with a great display and compatibility with most smart assistants. What's new? It adds built-in Alexa voice controls with impressive built-in mics and a speaker, so you can easily change the temperature with a few words. The fifth-generation model doesn't need a C wire, but it does come with a power extension kit that you'll need to wire to your furnace control board.
$249 at Amazon $250 at Best Buy
For high/line voltage systemsMysa Smart Thermostat
The rare smart thermostat that's compatible with 120V-240V, electric baseboard, and fan-forced heaters, the Mysa Smart Thermostat can mostly be installed yourself in a few minutes, is compatible with Alexa, Google, and HomeKit, and has all the smart tools you need to cut down on your energy usage. App scheduling, geofencing to track when you're away from home, pre-heating or pre-cooling based on your schedule, and in-depth energy reports for possible improvements.
$139 at Amazon $140 at Best Buy
Proceed with caution ...Google Nest Learning Thermostat - 3rd Generation
The Nest Learning Thermostat remains one of the smartest and useful thermostats today, supporting multiple zones, learned schedules, Alexa/Google Assistant integration, and HVAC monitoring. However, you may encounter power cycling issues if you install this without a C Wire, but Google has released a new Nest Power Connector as a C Wire substitute for consistent power. It's good enough to risk testing without a C wire, but keep the receipt just in case.
$230 at Amazon $250 at Best Buy $223 at Walmart
Check your voltageGoogle Nest Thermostat
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. It's entirely dependent upon whether your R and Y wires reach the voltage necessary to power everything; otherwise, your Nest Thermostat will shut down certain features to ensure the core temperature control still works. If your HVAC is fully compatible, it's a versatile and affordable machine that uses geofencing and motion tracking to detect when you're not home, saving you plenty of money. Otherwise, try installing the new Nest Power Connector and see if that solves your issues.
$130 at Amazon $130 at Best Buy $130 at B&H
Best brand, lowest costecobee Lite SmartThermostat
The ecobee 3 lite misses a few convenience features that the 5th-gen has, like a built-in occupancy sensor and built-in voice control. However, it's an excellent budget option, and you can still fully control your home's heating and cooling from anywhere in the world through the app or in your home with smart assistant devices. The ecobee3 lite also comes with the power extension kit to circumvent the need for a C wire.
$169 at Amazon $170 at Best Buy $170 at Ecobee
Middle of the roadecobee4 SmartThermostat
If you want to save a little money compared to the newest ecobee thermostat, the fourth-generation model is a nice mid-tier option - if you can still find it in stock. Like its 5th-gen successor, it has built-in Alexa and works with Google Assistant and HomeKit, is compatible with remote room sensors, and has identical energy savings. However, you'll just miss out on Alexa calling, Spotify connect, Bluetooth streaming, the 5.0 Wi-Fi band, and the newer model's nice glass display. If those seem superfluous for a thermostat, this is a slightly cheaper alternative.
$228 at Amazon$219 at Overstock$219 at Sears
Budget pickEmerson Sensi Wi-Fi Smart Thermostat for Smart Home (ST55)
If you don't mind a bit of a dated look and lack of a 24/7 light-up display, then Emerson's Sensi smart thermostat is your best budget pick. It only requires a C wire for heat- and cool-only systems (or heat pumps), and it still has full Wi-Fi connectivity, a straightforward app, easy program controls, and minimal setup required.
$110 at Amazon $129 at Home Depot $140 at Lowe's
For standalone AC unitsSensibo Sky - Smart Home Air Conditioner System
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 Sky controls your window or mobile AC appliances, letting you set up conditioning or heating schedules or pick specific temperatures through wifi monitoring. Plus, it makes your AC units controllable through Echo or Google Home commands.
No C wire? No problem (mostly)!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.
If you prefer a painless, battery-powered unit, the Nest Thermostat E is your best option - especially since it's so affordable compared to other thermostats. It has plenty of smart features like motion and multi-room sensing, Google Assistant and Alexa commands, and an auto-away model. By this point, it's a relatively old thermostat, and Google has mostly moved on to the new Nest Thermostat. Still, as we broke down in our Nest Thermostat E vs. Nest Thermostat article, the old dog has a few tricks that make it a better choice.
Whether your Nest or Nest Learning Thermostat will work with a Power Connector varies from home to home. For more consistency, consider ecobee instead.
Plus, a Nest Thermostat - or an older Nest Learning Thermostat (3rd Gen)- demands slightly more power than the Nest E and may be compromised without a C wire as a result. 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.
If you have a little electrical know-how (and a little extra cash), the ecobee SmartThermostat 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 difficult. 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 built-in Alexa 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, use a simple Venstar kit to install a new set of HVAC-compatible wires. With this tool installed, virtually any smart thermostat should be compatible with your home's heating and cooling.