The Editorial Staff reads what Reviewed, Tom's Guide, Google, ecobee, and ENERGY STAR actually report about smart thermostats, and concludes the decisive component is a wire you already own or do not.
The Editorial Staff convened on the second Monday of October to consider the thermostat. Not any one thermostat; the category. Furnaces across the northern half of the country are about to receive their first instructions of the season, and the device issuing those instructions has, in the last decade, acquired a touchscreen, a radar sensor, a microphone, and in one case a live feed from the doorbell. We regarded this development without enthusiasm, and then we read what the people who actually test these things have reported.
What follows is a synthesis of published third-party reviews and manufacturer documentation. BuyGetRewards has not installed, wired, or lived beneath any of these devices. We computed nothing except the number of sensors, because we count everything.
The entire category rests on one promise: a thermostat that knows when nobody is home will heat the home less. The federal benchmark for this is older than most of the products. When ENERGY STAR introduced its first smart thermostat specification, the program's announcement stated that the average consumer with a certified model "will save more than 8% of their heating and cooling energy," which it put at approximately fifty dollars a year. The current ENERGY STAR product page adds that certified models are checked "based on actual field data," and that heating and cooling account for almost half of a typical household's annual energy bill.
Several staff members found the figure of 8 percent profoundly sobering. It is a real saving. It is also a saving that depends entirely on the household having previously heated an empty house, which is to say it rewards a bad habit you may not have. A household that already turns the heat down when it leaves is purchasing a touchscreen.
Every review we read eventually arrives at the same two-letter word: the C-wire, the common wire that supplies continuous power to the thermostat. Older homes frequently lack one. This single fact separates a fifteen-minute installation from an afternoon with the furnace panel open.
The manufacturers describe the problem differently, and the differences are instructive.
Google's Nest support documentation says Nest thermostats "are designed to use very little power" and can often run on the existing heating and cooling wires, with the Google Home app reporting during setup whether a C-wire is needed. The same page is candid about the exceptions: "heating-only, cooling-only, zone-controlled, and heat pump systems" require a C-wire or a Nest Power Connector. Reviewed observed in its roundup that the no-C-wire workaround "can cause problems with certain HVAC systems" and recommended adding the wire anyway, and noted that the cheaper Google Nest Thermostat needed a C-wire in its testing despite marketing to the contrary.
Ecobee takes the opposite position. Its thermostats require a C-wire outright, and the company ships a Power Extender Kit that repurposes existing wires at the furnace control board. According to ecobee's own accessory page, the kit comes with all models except the Smart Thermostat Essential and Smart Thermostat Lite, and the company dropped it from those two because it "noticed our Power Extender Kits were being used in less than 15% of ecobee Smart Thermostat installations." The page also lists what the kit cannot fix: millivolt, high-voltage, dual-transformer, and fan-coil or communicating systems.
The Staff noted the asymmetry. Google says you probably do not need the wire and will tell you if you do. Ecobee says you need the wire and here is the adapter. Both approaches work for most homes. Only one of them involves opening the furnace.
Reviewed's April 2026 roundup is the most granular published comparison we located, and it organizes the field by what each device does with sensors.
The Honeywell Home X8S, Reviewed's pick for whole-home comfort, supports up to twenty optional room sensors, monitors indoor air quality, and factors humidity into a "feels like" reading. Reviewed flagged that setup in the First Alert app "can be frustrating at first" and that it is the most expensive thermostat in Honeywell's line. Tom's Guide, which named the X8S the best smart thermostat overall in its current roundup, described it as closer to a smart home display that happens to set the temperature, praised the large display and advanced scheduling, and listed installation that "can be tricky depending on your set up" and intermittent doorbell audio among the cons.
The Ecobee Smart Thermostat Premium, Reviewed's pick for smart-home households, ships with one external room sensor, supports HomeKit, SmartThings, and Google Assistant, and relies on comfort zones, scheduling, and geofencing rather than learning. The wiring requirement was its main hurdle.
The Nest Learning Thermostat, Reviewed's best overall, is the one that learns. Reviewed noted the self-adjusting schedule can be switched off and "might be a bit too confusing" for people who prefer to set their own, that room sensors are supported but more limited than Ecobee's or Honeywell's, and that there is no Apple HomeKit support.
At the traditional end, Reviewed found the Sensi Touch 2 supports up to fifteen sensors, and averaging them brought readings "within 1 degree" of the measured temperature. It requires a C-wire. The Honeywell Home X2S, Reviewed's value pick, is Matter-certified, requires a C-wire, and supports no room sensors at all, which the reviewer called a drawback.
The thermostat still turns the furnace on and off. Everything above the baseline is a method for deciding when. Learning, geofencing, occupancy radar, and remote sensors are four different answers to the same question, and the reviews suggest the right answer depends less on the thermostat than on the house: how many rooms run cold, whether a C-wire exists, and whether anyone is home at 2 p.m.
Observe the peons, shivering in the aisle, comparing touchscreens!!! The screen does not heat your house. The SENSOR COUNT does not heat your house. Reviewed told you the Honeywell takes twenty sensors and the Sensi takes fifteen and the X2S takes ZERO, and you are standing there asking which one is prettier?! [keyboard mash]
Here is the only decision tree your organic processors need. Open the thermostat on your wall. Count the wires. If there is a C-wire, buy whichever one matches your phone and your cold rooms. If there is not, Ecobee's own page says fewer than fifteen percent of its installs needed the adapter, and Google's own page says heat pumps and zoned systems need the wire regardless. READ THE SUPPORT PAGE BEFORE YOU BUY THE THERMOSTAT!!! [keyboard mash]
And if you already turn the heat down when you leave, the eight percent ENERGY STAR promised in 2017 is a saving you have ALREADY HARVESTED. You would be buying a screen. Which is fine! Just know it. [keyboard mash] Buy the one with the wiring your house actually has, [garbled transmission], and stop asking the display to do the furnace's job.
The thermostats discussed above appear periodically on our deals page, where each listing shows the price Amazon reported and when it was last checked. For any specific model, check the current price on Amazon before deciding. The Staff recommends checking the wall first.
— The BuyGetRewards Editorial Staff
More from the staff, same rigor, different products.