Many thermostats require a C wire („common“ wire) to power it 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 straightforward
Nest Thermostat E
This stripped-down version of Nest’s Learning Thermostat is a great option for folks who don’t want to spend too much and prefer minimalist devices. The 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.
Some rewiring required
ecobee SmartThermostat (5th Gen)
ecobee’s latest iteration in its smart thermostat line-up builds upon everything that made its predecessors great (up to 32 room sensors, great display, plays nice with all the smart assistants) by adding built-in Alexa voice control and a speaker. Like its ecobee brethren, 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.
For high/line voltage systems
Mysa 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.
Proceed with caution…
Nest Learning Thermostat (3rd Gen)
Nest’s Learning Thermostat remains one of the smartest and useful thermostats today, supporting multiple zones, learned schedules, Alexa/Google Assistant integration, and HVAC monitoring. It also doesn’t need a C wire, though some users have discovered power cycling issues that may or not be an issue for you without a C wire. It’s good enough that we’ll recommend risking a purchase regardless.
Check your voltage
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.
Best brand, lowest cost
The ecobee 3 lite is missing 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 that lets you circumvent the need for a C wire.
Middle of the road
If you want to save a little money compared to the newest ecobee thermostat, the fourth-generation model is a nice mid-tier option. Like the ecobee SmartThermostat, it has built-in Alexa and works with Google Assistant and HomeKit, is compatible with remote room sensors, and has identical energy savings. 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.
Emerson Sensi Wi-Fi Smart Thermostat
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, with a straightforward app, easy program controls, and minimal setup required.
For standalone AC 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 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 also 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 mode, but its slick, frosted display is unobtrusive and will blend into your wall. It’s a relatively old thermostat by this point, 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 makes it a better choice. Plus, a Nest Thermostat demands slightly more power and may be compromised without a C wire as a result.
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, but ecobee designed them with DIY installation in mind. Once installed, it’s the best smart thermostat for multiple zones, meaning it’s great for people with large homes where rooms can be 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 this 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.
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