The C wire (“common” wire) is the wire that provides continuous power to your thermostat. Older thermostats didn’t need it because they were simple on/off affairs, but smart thermostats need continuous power due to their LED displays and Wi-Fi-powered advanced functions. 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 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 things to be minimalist. 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.
$170 at Best Buy
$140 at Walmart
$170 at B&H
Nest Learning Thermostat (third generation)
Nest’s Learning Thermostat was first on the scene, and its third generation has improved upon that original formula with a powerful feature set, gorgeous display, and multiple color options. This one doesn’t need a C wire, though I have read about some power cycling issues that may or not be an issue for you. It may be worth the risk for the excellent learning capabilities and Alexa/Google Assistant integration.
$219 at Amazon
$220 at Best Buy
$220 at Walmart
Some rewiring required
ecobee SmartThermostat (5th generation)
ecobee’s latest iteration in its smart thermostat line-up builds upon everything that makes 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 5th-gen 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.
$199 at Amazon
$250 at Best Buy
$249 at Walmart
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.
$169 at Amazon
$170 at Best Buy
$170 at Apple
Emerson Sensi Wi-Fi Smart Thermostat
If you don’t mind a bit of a dated look and lack of 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.
$90 at Amazon
$129 at Newegg
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.
$115 at Amazon
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, the options above offer solid alternatives. 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; you’ll have to decide which of those smart thermostat options sounds better to you.
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.
If you do, however, have a little electrical know-how (and a little extra cash), the ecobee SmartThermostat is the best smart thermostat money can buy, and the power extension kit makes life much easier. From its gorgeous display to its multiroom sensor integration, built-in Alexa, and solid speaker (that will even let you play your Spotify jams!), 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 C wire.