Smart Thermostats: How They Work, What They Save and Which to Buy

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It’s a cold January morning. You left for work at seven and the furnace kept the empty house at 70°F all day, the way it does every day. Across the street, your neighbor’s thermostat noticed the house was empty, eased the heat down a few degrees, and started warming it back up when her phone left the office. She walked into a warm living room and a slightly smaller bill. She didn’t touch a thing. That’s the whole idea of a smart thermostat.

In short: a smart thermostat is a Wi-Fi thermostat that adjusts your heating and cooling on its own, using schedules, occupancy sensing and your phone’s location. ENERGY STAR says certified models save about 8% of heating and cooling bills on average, roughly $50 a year, and more in homes that sit empty during the day. Good ones cost about $80 to $280, and many utilities offer rebates.

This page starts our Smart Thermostats section: how they work and save energy, whether one will work with your system (C wire, heat pump, mini split, baseboard), the features worth paying for, installation, costs and rebates, and our picks, with links to every guide in the section.

Smart thermostats at a glance

• What it is: a thermostat with Wi-Fi, an app and software that sets back the temperature when you’re asleep or away, without you having to program it perfectly.
• What it saves: about 8% of heating and cooling bills on average, or about $50 a year, per ENERGY STAR’s field data. Your result depends on your climate, your habits and your system.
• Works with: most 24-volt central systems (gas, oil or electric furnaces, central air, heat pumps, many boilers). Not with line-voltage electric baseboard heaters, and not with ductless mini splits, which need their own kind of controller.
• The C wire: many smart thermostats need a “common” wire for steady power. Some include an adapter, and Google says its Nest thermostats work without one in most homes.
• Cost: about $80 (Amazon Smart Thermostat, Sensi Lite) to about $280 (Nest Learning Thermostat with sensor), seen October 2026.
• Money back: there’s no federal tax credit for a smart thermostat in 2026, but many utilities offer rebates, instant discounts or bill credits. Check your utility and the ENERGY STAR Rebate Finder.

What is a smart thermostat?

A thermostat is a switch with a temperature sensor. When the room drops below your setting, it closes a circuit that tells the furnace or heat pump to run; when the room gets there, it opens the circuit. A programmable thermostat adds a clock, so you can set different temperatures for night, day and evening. A smart thermostat adds a Wi-Fi connection, an app and software that does the programming for you, or at least helps.

The difference matters because programmable thermostats only save energy if people actually program them and stick with it, and many don’t. Smart models fill that gap in a few ways:

• Learning or suggested schedules: Nest’s Smart Schedule learns the temperatures you choose at different times; ecobee’s schedule assistant and Nest’s Savings Finder suggest small changes in the app.
• Occupancy sensing: motion or radar sensors in the thermostat (and in remote room sensors on some models) notice when nobody’s home.
• Geofencing: the app uses your phone’s location to switch to an away temperature when everyone has left and back when someone is heading home.
• Remote control: forgot to turn the heat down before a weekend away? Do it from your phone.
• Energy reports and alerts: monthly runtime reports, filter reminders, and warnings if the house gets too hot or cold.
• Utility programs: many can join your utility’s demand-response program (Nest calls it Rush Hour Rewards, ecobee calls it Community Energy Savings), which nudges the temperature during peak hours in exchange for credits.

Want the full comparison? Read smart vs programmable thermostat.

How much does a smart thermostat save?

The honest answer is “some, and it depends on you.” Here is what the independent sources say:

• ENERGY STAR: certified smart thermostats save about 8% of heating and cooling bills on average, or about $50 a year. Certification is based on real-world data from a large sample of homes using each product, not a lab test.
• U.S. Department of Energy: you can save as much as 10% a year on heating and cooling by turning your thermostat back 7 to 10°F for 8 hours a day from its normal setting. A smart thermostat simply makes that setback automatic.
• Why it matters: ENERGY STAR notes that almost half of a home’s annual energy bill goes to heating and cooling, more than $900 a year.

Makers quote bigger numbers. ecobee says its thermostats can save “up to 26%” on heating and cooling costs, and Google cites studies showing 10 to 12% on heating and about 15% on cooling for Nest. Those are “up to” and best-case figures from the makers; we lean on the ENERGY STAR average.

Here’s what that looks like in dollars. These are our estimates, not promises: annual heating and cooling cost × savings percentage.

Your yearly heating + cooling cost	At 8% (ENERGY STAR average)	At 10% (DOE setback figure)	Payback on a $130 thermostat (at 8%)
$600	about $48	about $60	about 2.7 years
$900	about $72	about $90	about 1.8 years
$1,500	about $120	about $150	about 1.1 years
$2,200	about $176	about $220	under 1 year

Who saves the most? Homes that sit empty for long stretches, people who never used the old thermostat’s schedule, and homes with high heating or cooling bills. Who saves the least? Someone who already turns the heat down every night and every morning by hand, or a home that’s occupied all day. We go deeper in do smart thermostats save money?

Will a smart thermostat work with your system?

This is the question to answer before you buy anything. Take the cover off your current thermostat (most pop off) and look at the wires and the labels on the terminals. Then match your home to one of these:

Your heating and cooling	What you’ll see	What works
Central furnace and AC (gas, oil or electric)	Thin wires on terminals like R, W, Y, G, C	Almost every smart thermostat
Central heat pump	An O/B terminal, often AUX or E too	Most, but check heat pump stages and aux heat support
Boiler or radiant (low voltage)	Two thin wires, often R and W	Many; often needs a C wire or adapter
Electric baseboard	Thick wires, wire nuts, a label saying 120 V or 240 V	Only line-voltage smart thermostats (like Mysa for baseboard); an electrician is recommended
Ductless mini split, window or portable AC	A handheld infrared remote, no wall thermostat	Plug-in infrared controllers like Mysa for mini splits or Cielo Breez

Every major brand has an online compatibility checker that asks you which labels you see: use it. If your thermostat’s wires are thick and connected with wire nuts, stop: that’s line voltage, which can shock you, and it needs a thermostat built for it, installed by a licensed electrician.

The C wire, explained

A Wi-Fi thermostat with a screen needs a little power all the time. In a 24-volt system, that steady power comes through the C (“common”) wire. Older homes often don’t have one connected, because a basic thermostat didn’t need it. Your options:

• Look behind the wall plate: sometimes there’s an unused wire tucked in the wall that can serve as a C wire (connected at the furnace end too).
• Use the included adapter: the ecobee Premium and Enhanced include a Power Extender Kit; on the ecobee Essential it costs extra.
• Pick a model that doesn’t need one: Google says Nest thermostats use Power Sharing and work without a C wire in the vast majority of homes; for the Nest Learning Thermostat (4th gen) it puts the exceptions at under 1%. Some systems, including heat pumps, heating-only and cooling-only, still need a C wire or the Nest Power Connector.
• Avoid models that always need one if you don’t have it: the Amazon Smart Thermostat and Sensi Touch 2 require a C wire.

Our best smart thermostat without a C wire guide walks through each option.

Smart thermostats and heat pumps

Heat pumps need extra care. The Department of Energy has long warned that setting back an ordinary thermostat on a heat pump can backfire: when the house has cooled down a lot, the thermostat may call for the backup electric resistance heat (“aux” or “emergency” heat) to catch up quickly, and that backup heat costs far more to run than the heat pump itself. DOE notes that thermostats designed for heat pumps use special logic to keep backup heat use to a minimum.

What to look for:

• Support for your stages: the Nest Learning Thermostat (4th gen) controls heat pumps with auxiliary and emergency heat (O/B, AUX, E); the ecobee Premium supports heat pumps with 2 stages plus 2 stages of aux heat, the Enhanced 2 stages plus 1 stage of aux.
• An aux heat lockout: a setting that keeps the backup heat off above an outdoor temperature you choose. Nest lists an aux lockout range of 0 to 70°F; ecobee has threshold settings for the same job.
• Dual fuel: if your heat pump has a gas furnace as backup, look for a dual-fuel “balance point” setting. Nest’s runs from 10 to 50°F.
• Gentle setbacks: with a heat pump, smaller setbacks (a few degrees) with an early start usually make more sense than big swings.

If your heat pump was installed recently, ask the installer which thermostat settings they recommend; some heat pumps work best, or only fully, with the maker’s own communicating thermostat. See the best smart thermostat for a heat pump and our heat pumps section.

Mini splits, window ACs and baseboard heat

A ductless mini split doesn’t use a wall thermostat at all: each indoor head is controlled by an infrared remote. For these, a plug-in “smart thermostat” learns your remote’s signals and replaces it. The Mysa for mini splits ($139 at Mysa, October 2026) plugs into a regular outlet, needs a line of sight to the indoor unit and 2.4 GHz Wi-Fi, and Mysa says it works with most mini splits, window and portable ACs that use a remote with a display. The Cielo Breez Max does the same job. One per indoor unit. More in the best smart thermostat for a mini split.

Electric baseboard heaters run on 120 or 240 volts through the thermostat itself. They need a line-voltage smart thermostat such as Mysa’s baseboard model, one per heater or zone. Line-voltage wiring can kill: turn off the breaker, and if you’re not completely comfortable, hire a licensed electrician.

Features worth paying for (and ones you can skip)

• Room sensors (worth it in two-story or drafty homes): a thermostat in the hallway doesn’t know the back bedroom is freezing. Remote sensors let the system aim for the rooms you’re actually in. The ecobee Premium and the Nest Learning Thermostat (4th gen) bundle include one sensor; others sell them separately.
• Occupancy sensing (worth it): it’s what lets the thermostat save energy without you thinking about it. The ecobee Premium and Enhanced use radar; Nest uses a Soli radar sensor for motion.
• Geofencing (worth it for busy households): works best when everyone in the home has the app.
• Smart home fit (depends): pick one that works with what you already use. Nest is built for Google Home and is Matter-certified; ecobee works with Apple HomeKit, Alexa, Google Assistant and SmartThings; the Amazon Smart Thermostat runs through the Alexa app.
• Built-in speaker and voice assistant (nice, not needed): the ecobee Premium has Alexa built in. It doesn’t save energy.
• Air quality monitor (nice to know): the ecobee Premium reports indoor air quality and reminds you about filters.
• Subscriptions (usually skip): none of the thermostats we recommend require a subscription to run the thermostat. ecobee’s paid Smart Security plans are for its security features, not heating and cooling. See smart thermostats without a subscription.

One more thing to weigh: how long the maker supports old hardware. Google ended app support for the first- and second-generation Nest Learning Thermostats on October 25, 2025. They still work as basic thermostats, but no longer connect to the app. A thermostat lasts many years, so a maker’s track record is part of the price.

Installing a smart thermostat

On a standard 24-volt system, many people install a smart thermostat themselves in under an hour, guided by the app. The basic steps:

1. Run the maker’s compatibility check with a photo of your current wiring.
2. Turn off power to the heating and cooling system at the breaker (and the furnace switch, if there is one). Confirm the old thermostat’s screen is dead.
3. Take a clear photo of the wires on their terminals, then label each wire with the stickers in the box.
4. Remove the old thermostat, mount the new base, connect each wire to the matching terminal, and attach the C wire adapter if you need one (it usually goes in at the furnace’s control board).
5. Turn the power back on, follow the app’s setup, and test heat, cool and fan.

Call an HVAC pro if your wiring doesn’t match the checker, if you have a heat pump with several stages, a zoned system, a communicating system, or anything with thick line-voltage wires. Old mercury thermostats (a glass bulb inside) shouldn’t go in the trash: take them to a household hazardous waste or thermostat recycling drop-off. And if the thermostat can’t reach Wi-Fi or loses its schedule, check where it hangs: DOE advises an interior wall away from direct sunlight, drafts, doorways, skylights and windows, with no furniture blocking airflow.

What smart thermostats cost, and rebates in 2026

Prices we saw in October 2026: the Amazon Smart Thermostat about $80, Sensi Lite about $90, ecobee Smart Thermostat Essential about $110 on sale ($140 regular), Google Nest Thermostat about $130, ecobee Enhanced about $165 on sale ($200 regular), ecobee Premium about $210 on sale ($260 regular), and the Nest Learning Thermostat (4th gen) with sensor about $280. Professional installation, if you want it, is extra.

Rebates: many utilities pay part of the cost of an ENERGY STAR certified smart thermostat, sell them at a discount in their own online marketplaces, or pay a bill credit when you enroll in their demand-response program. Amounts and rules vary by utility and change often, so check:

• your electric and gas utility’s website (search “your utility smart thermostat rebate”);
• the ENERGY STAR Rebate Finder (enter your ZIP code);
• the ecobee and Google Nest rebate finders on their own sites.

There’s no federal tax credit for a smart thermostat in 2026. We keep a running guide in smart thermostat rebates and a broader one in home energy rebates.

The best thermostat settings, quickly

DOE’s starting point: about 68°F in winter while you’re awake and home, lower while you’re asleep or away; about 78°F in summer while you’re home, higher while you’re away. Turning back 7 to 10°F for 8 hours a day can save up to 10% a year on heating and cooling. Comfort comes first, especially for babies, older people and anyone with health conditions, so adjust from there. Our best thermostat settings for winter and summer guide has the details, including heat pumps.

Our top smart thermostat picks

Prices change often. The prices below are what we saw at the maker or a major retailer in October 2026; check the current price before you buy.

ecobee Smart Thermostat Premium is the most complete package: a remote SmartSensor and Power Extender Kit in the box, radar occupancy sensing, support for heat pumps with two stages of aux heat, and a 3-year warranty. Google Nest Learning Thermostat (4th gen) is the pick for Google Home households and for homes without a C wire. ecobee Enhanced gives you most of the Premium’s brains for less. Amazon Smart Thermostat is the cheapest way in if you have a C wire and use Alexa. The full rankings are in the best smart thermostats of 2026, and the two big brands go head to head in ecobee vs Nest.

Which smart thermostat guide do you need?

If you…	Read
Want the short list of the best models	Best smart thermostats 2026
Are choosing between the two big names	ecobee vs Nest
Have a heat pump	Best smart thermostat for a heat pump
Don’t have a C wire	Best smart thermostat without a C wire
Hate monthly fees	Best smart thermostat without a subscription
Have a ductless mini split	Best smart thermostat for a mini split
Already own a programmable thermostat	Smart vs programmable thermostat
Want to know if it pays off	Do smart thermostats save money?
Want the right temperatures	Best thermostat settings, winter and summer
Want money back	Smart thermostat rebates

Keep exploring

A smart thermostat is one of the cheapest steps in a bigger plan. Pair it with sealing drafts and the other ideas in how to lower your electric bill, and if your furnace or AC is near the end of its life, start with our heat pumps section. To understand the physics of heating a home, see thermal energy and electrical energy; for the bigger picture, green energy. Every guide in this section lives in the smart thermostats category.

Smart thermostat questions

Is a smart thermostat worth it?

For most homes with central heating or cooling, yes. ENERGY STAR puts the average saving at about 8% of heating and cooling bills, around $50 a year, and more if the house is often empty. With a utility rebate, many pay for themselves in a few years. If you already set back your temperature by hand every day, the savings will be smaller.

Do I need a C wire for a smart thermostat?

It depends on the model. The Amazon Smart Thermostat and Sensi Touch 2 need one. The ecobee Premium and Enhanced include an adapter for homes without one. Google says Nest thermostats work without a C wire in most homes, though some systems, including many heat pumps, still need a C wire or the Nest Power Connector.

Can I install a smart thermostat myself?

On a standard 24-volt system, usually yes: turn off the power at the breaker, photograph and label the wires, and follow the app. Hire an HVAC pro for multi-stage heat pumps, zoned or communicating systems, or anything that doesn’t match the maker’s compatibility checker. Line-voltage baseboard thermostats are best left to a licensed electrician.

Do smart thermostats work with heat pumps?

Most do, including the ecobee and Nest models we recommend. Check that the model supports your stages and aux heat, and set an aux heat lockout so the expensive backup heat doesn’t switch on when the heat pump could do the job. DOE warns that big setbacks on a heat pump can cancel your savings.

Do smart thermostats need a subscription?

Not the ones we recommend. ecobee, Nest, Amazon, Sensi and Mysa thermostats control your heating and cooling with no monthly fee. ecobee sells optional Smart Security plans, and Google sells Google Home Premium, mainly for cameras and security, not for the thermostat.

What happens to a smart thermostat when the Wi-Fi goes down?

It keeps heating and cooling on its schedule; you just lose remote control from your phone and features that rely on the internet, such as geofencing, until the connection returns. You can always change the temperature on the thermostat itself.