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The 7 best smart thermostats, sorted by the wires you have
Updated
Short version: if you have no C wire, the ecobee Premium is the easy call, because the listing says its adapter kit is in the box. With a plain furnace and AC and no C wire, the Nest Thermostat and the Sensi ST55 are built to run without one. If you already have a C wire, every 24 volt pick here is open to you, so choose by platform. Electric baseboards need the Mysa and nothing else on this page.
Not sure what you have? Run the wire checker first.
Safety first. Turn off power at the breaker or the system switch before you pull a thermostat off the wall, then change the set temperature by 5 degrees and wait 5 minutes to confirm nothing starts. If you see thick wires, wire nuts, L1 or L2, or a 120 V or 240 V label, stop. That is line voltage. Put the cover back and call a licensed electrician.
Quick comparison
| Model | Needs a C wire? | No C wire: system types it fits from the box | Room sensor | Works with |
|---|---|---|---|---|
| ecobee Smart Thermostat Premium | C wire, or the Power Extender Kit in the box | 2 of 4 | One included | HomeKit, Alexa, Google |
| ecobee Smart Thermostat Essential | C wire, or the Power Extender Kit sold separately | 0 of 4 | Unclear, see the sensor guide | HomeKit, Alexa, Google |
| Google Nest Learning Thermostat (4th gen) | Not in most homes per the listing. App checks power in setup | 1 of 4 | One included | Google, Alexa, Siri, Matter |
| Google Nest Thermostat | Not in most homes. Yes for heat only, cool only, zoned and heat pump | 1 of 4 | Not on Google's list | Google, Matter |
| Sensi Smart Thermostat ST55 | Not on most furnace plus AC systems. Yes for heat only, cool only, heat pump and HomeKit | 1 of 4 | None on this model | Alexa, HomeKit, Google, SmartThings |
| Amazon Smart Thermostat | Always: C wire or an adapter kit sold separately | 0 of 4 | Uses select Echo devices | Alexa only |
| Mysa Smart Thermostat V2 for Baseboards | Does not apply. Line voltage, needs 4 or more wires | Line voltage | None listed | HomeKit, Alexa, Google |
The third column is our count, using the checker's rules, across four example homes with no C wire: furnace plus AC, heat pump, cool only and heat only. It counts only what comes in the box. It is our reading of maker pages, not a maker claim.
- Furnace and AC five wires with C6 picks
- Furnace and AC four wires no C3 picks
- Heat pump with aux heat five wires no C0 picks
- Cool only three wires no C0 picks
- Heat only furnace or boiler two wires0 picks
The picks
Specs and owner feedback checked on Amazon September 19, 2026. C wire rules come from each listing and from the maker support pages listed under Sources.
ecobee Smart Thermostat Premium
Get this if your old thermostat has no C wire and you want the fix included. The listing says the Power Extender Kit is in the box, along with one SmartSensor for another room. Skip it if you have a heat only boiler with two wires. ecobee says the kit does not work on heat only or two transformer systems, so those need a real C wire. Skip it for baseboard heat too. The listing's spec table names electric baseboard heaters, but ecobee's support page says high voltage systems are not compatible.
Key specs (from the manufacturer listing)
- Power Extender Kit for homes without a C wire is included, per the listing
- One SmartSensor included. Works with Apple HomeKit, Alexa and Google Assistant per the listing
- Maker claims it is compatible with 95 percent of HVAC systems
- ecobee support: up to 2 heat and 2 cool stages, heat pumps with up to 2 aux stages, dual fuel
- Smoke alarm listening needs an ecobee Smart Security subscription, per the listing
- ENERGY STAR certified, 3 year maker warranty, 24 volts
Recurring themes in owner feedback
- They like: Owners say installation and wiring are simple, and they like the interface and the vacation settings. Many say it ties in well with their smart home.
- They complain about: Some report trouble keeping the room sensor connected. Some say it reads a few degrees high or does not always reach the set temperature, and the summary we read flagged product quality complaints.
Good
- Adapter and a room sensor are in the box
- Widest stage support of the ecobee picks
- Longest warranty we saw with the Sensi
Watch out for
- Kit does not cover heat only or two transformer systems
- Some owners report sensor connection trouble
- One feature on the listing needs a subscription
ecobee Smart Thermostat Essential
Get this if you already have a C wire, a plain one stage system, and want HomeKit, Alexa and Google in a small ecobee. Skip it if you have no C wire and do not want to buy a second part. The listing says the Power Extender Kit and trim kit are sold separately. Skip it for a two stage heat pump as well. ecobee says the Essential supports one heat pump stage and one aux stage.
Key specs (from the manufacturer listing)
- Power Extender Kit is sold separately, per the listing
- Maker claims it is compatible with 85 percent of systems
- Listing: conventional 2H/1C or 1H/2C, heat pump 2H/1C, boilers, dual fuel
- Works with Apple HomeKit, Google Assistant and Alexa per the listing
- Listing says a SmartSensor can be added. ecobee's sensor FAQ does not list the Essential as compatible
- ENERGY STAR certified, color touchscreen, 3.2 ounces
Recurring themes in owner feedback
- They like: Owners call the install straightforward and like setting temperature ranges and schedules from a phone.
- They complain about: Temperature hold and Wi-Fi get split reports. Some say it drops off Wi-Fi, and some report units failing suddenly.
Good
- Small and light
- All three big voice platforms
- Schedule and energy tracking in the app
Watch out for
- No adapter in the box
- Fewer stages than the Premium
- Sensor support is unclear between the listing and ecobee's FAQ
Google Nest Learning Thermostat (4th gen) with sensor
Get this if you have a multi stage system or want a room sensor included and Matter support. Google says the 4th gen handles up to 3 heat and 2 cool stages on a conventional system. Skip it if you have dual fuel and planned to install it yourself. Google says dual fuel needs a trained pro. The listing says no C wire is required in most homes, and the Google Home app checks power during setup. If it comes up short, the fix is a C wire or the Nest Power Connector, which is sold separately.
Key specs (from the manufacturer listing)
- Listing: works with most 24V systems, no C wire required in most homes
- Google support: up to 3 heat and 2 cool stages, or 2 heat pump stages plus 2 alternate heat stages
- Nest Temperature Sensor (2nd gen) included. Up to 6 sensors per thermostat per Google
- Matter compatible. Works with Alexa, Siri and Google Assistant per the listing
- AQ terminals for a humidifier, dehumidifier or ventilator per Google
- 5.7 ounces, one CR2 battery included
Recurring themes in owner feedback
- They like: Owners like the modern look, the easy install and the interface. Some say it is smart about when to heat and cool.
- They complain about: Some say it reads 2 degrees or more off the real room temperature. Reports on the app are mixed.
Good
- Supports the most stages of the picks here
- Sensor included
- Matter support
Watch out for
- Some owners say it reads a couple of degrees off
- Power Connector costs extra if you need it
- We did not see a warranty length on the listing
Google Nest Thermostat
Get this if you have a plain furnace and air conditioner, four wires and no C. The listing says it is designed to work without a C wire in most homes. Skip it, or plan on an extra part, if you have a heat pump, heat only, cool only or zoned system. The same listing says those need a C wire or a compatible power accessory. Skip it if you want room sensors. Google's sensor page lists the Learning Thermostat and the Thermostat E, not this model.
Key specs (from the manufacturer listing)
- Listing: no C wire in most homes. Heating only, cooling only, zone controlled and heat pump systems need a C wire or power accessory
- Matter certified voice assistants and Google Assistant per the listing
- Wi-Fi on 2.4 GHz and 5 GHz, Bluetooth Low Energy
- Two batteries included
- ENERGY STAR certified, 1 year maker warranty
- 3.3 inches wide, 5 ounces
Recurring themes in owner feedback
- They like: Owners are positive on what it does day to day, and some found setup very easy.
- They complain about: Others found the install tricky. Wi-Fi connection problems come up often, and reliability gets split reports.
Good
- The listing states its C wire exceptions plainly
- Matter support
- Google offers an online compatibility checker
Watch out for
- Not on Google's list for the Nest Temperature Sensor
- Owners often report Wi-Fi trouble
- Shorter warranty than ecobee Premium or Sensi
Sensi Smart Thermostat ST55
Get this if you want buttons, a familiar shape that covers the old paint outline, and a furnace plus AC system with no C wire. Skip it, or plan on a C wire, if you have a heat pump, a heat only or a cool only system. Sensi's support page says those need one. It also says HomeKit needs a C wire on any system. Sensi says without a C wire on a heat only or cool only system, Wi-Fi drops out after about two hours.
Key specs (from the manufacturer listing)
- Listing: C wire not required in most applications
- Sensi support: C wire required for heat only, cool only, heat pump, and for HomeKit
- Works with Alexa, Apple HomeKit, Google Assistant and SmartThings per the listing
- Sensi support: works with whole home humidifiers and dehumidifiers
- Two AA batteries included. 24 volts AC
- ENERGY STAR certified, 3 year warranty, 5.88 inches wide
Recurring themes in owner feedback
- They like: Owners say it is easy to install and use, holds temperature accurately, and has a friendly app. Many call it reliable.
- They complain about: The review summary we read was mostly positive. The main tradeoff: Wi-Fi is mixed, with some owners reporting frequent disconnections.
Good
- Wide body hides the old thermostat's footprint
- Maker says it will not sell your personal information
- Owner summary was mostly positive
Watch out for
- HomeKit needs a C wire
- No wireless room sensors on this model per Sensi
- Some owners report Wi-Fi disconnections
Amazon Smart Thermostat
Get this if you have a C wire and you already run your home on Alexa. Skip it if you have no C wire and do not want extra work. The listing says it requires a C wire or a power adapter kit, which is sold separately. Skip it if you use HomeKit or Google Home. The listing only names Alexa, and the thermostat has no microphone, so voice control needs an Echo or another Alexa device.
Key specs (from the manufacturer listing)
- Listing: requires a C wire or a power adapter kit (sold separately)
- Listing: works with 24V systems such as forced air, heat pump and radiant boiler. Not 110 to 240V systems
- Alexa app and Alexa voice control. No built in microphone
- Wi-Fi on 2.4 GHz only
- Listing says it is made with Honeywell Home thermostat technology
- ENERGY STAR certified, 1 year limited warranty, 3.86 ounces
Recurring themes in owner feedback
- They like: Some owners say it performs well and like setting different temperatures for different times of day.
- They complain about: Many report Wi-Fi connection issues. Some say it does not hold the set temperature, Alexa control gets split reports, and several say it stopped working within two months.
Good
- Plain three button face
- Guided install in the Alexa app
- Can use readings from select Echo devices per the listing
Watch out for
- Always needs a C wire or an adapter
- Alexa only
- Owners report Wi-Fi issues and some early failures
Mysa Smart Thermostat V2 for Electric Baseboard Heaters
Get this only if you have line voltage electric heat: baseboards, fan forced heaters or similar on 120 to 240 volts. It is the one pick here made for thick wires. Skip it for any furnace, boiler or heat pump with thin wires labeled R, W, Y or G. Mysa says it needs at least four wires in the wall box and does not work on two wire installs. This is line voltage work. Hire a licensed electrician unless you are qualified to do it.
Key specs (from the manufacturer listing)
- Listing: line voltage only, 120 to 240V baseboards and fan forced heaters
- Listing: loads up to 1,900 W at 120V or 3,800 W at 240V
- Listing: needs at least four wires, including a neutral or second live wire
- Works with Alexa, Google Assistant and Apple HomeKit per the listing
- Heating only. Humidity sensor and touchscreen per the listing
- 3.5 x 5.1 inches, 1.12 pounds, wire nuts included
Recurring themes in owner feedback
- They like: Owners say it is easy to install with clear steps in the app, and they like the HomeKit tie-in and the scheduling.
- They complain about: Some report trouble adjusting temperature, and several report Wi-Fi connection failures.
Good
- Made for the wiring every other pick here rejects
- HomeKit, Alexa and Google
- Owners say the app walks them through the install
Watch out for
- No use on 24 volt systems
- Two wire installs are out
- Each unit only controls the heaters wired to it
Even the makers do not claim every home
ecobee puts a number on it. The Premium listing claims compatibility with 95 percent of HVAC systems, the Essential listing 85 percent. The gap tracks what we found: fewer stages, and no adapter kit in the box.
- ecobee Premium95 percent
- ecobee Essential85 percent
ENERGY STAR and utility rebates
ENERGY STAR says certified smart thermostats are independently certified, based on field data, to deliver energy savings. The six 24 volt picks here all say ENERGY STAR certified on their listings. Savings percentages on listings are maker claims, and they depend on how you set your schedule.
ENERGY STAR also says certified models are designed to work with programs some local utilities offer. Many utilities give a rebate on a certified thermostat. Check your utility, or enter your zip code in the ENERGY STAR Rebate Finder, before you buy. Some rebates only cover certain models.
Before you buy any smart thermostat
- Look behind the old one. Power off, pull the face, take a photo of the terminals. See what the wire labels mean.
- Read the C wire line on the listing. "Most homes" has exceptions. See the no C wire fine print.
- Check what is in the box. Only one pick here includes its adapter. See adapter options.
- Buy the same brand for very high end equipment. ENERGY STAR notes that for the very highest efficiency systems you may want a controller from the same company.