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 rewire your home.

Simple and straightforward Nest Thermostat E

Staff pick

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.

$136 at Amazon $130 at Best Buy $169 at B&H

The O.G. Nest Learning Thermostat (3rd Gen)

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.

$249 at Amazon $250 at Best Buy $239 at Walmart

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.

$249 at Amazon $250 at Best Buy $215 at Walmart

New bargain model Nest Thermostat

Google let the newest Nest Thermostat ditch school. It no longer learns from your heating habits and builds a schedule for you. You'll have to do it yourself. This thermostat uses Soli tracking and geofencing to register when you're in the room, activate the display when you're home, and turn down the air while you're away. This is undoubtedly the most stylish Nest thermostat, and it will still help you save money on your energy bill without costing so much upfront.

$130 at Best Buy $130 at B&H

Best brand, lowest cost ecobee3 lite

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.

$132 at Amazon $170 at Best Buy $170 at Apple

Middle of the road ecobee4

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.

$214 at Amazon

Budget pick 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.

$78 at Amazon $140 at Walmart

For standalone AC units Sensibo Sky

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 $120 at Walmart

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 will still power your home without C wires. 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. It's a relatively old thermostat by this point, and Google has mostly moved on to the new Nest Thermostat, but 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.

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 new set of HVAC-compatible wires.

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