A smart thermostat lowers heating and cooling bills only when it stops your system from running for an empty or sleeping house. Wiring fit and how reliably it sets back the temperature matter more than the brand.
Expect modest but real savings: certified models average about 8% on heating and cooling, roughly $50 a year. Choose in this order: compatibility with your heating system and wiring, how predictable your schedule is, and whether some rooms run hotter or colder than others.
What a Smart Thermostat Actually Saves
Heating and cooling account for nearly half of a typical home’s energy use, so a single-digit percentage cut still adds up. Homes left empty during the workday save the most, approaching $100 a year.
ENERGY STAR wrote its smart thermostat specification partly to replace the 10% to 20% savings claims common in early marketing with measured field results. Treat any bigger promise with suspicion.
Savings come from setbacks: the Department of Energy says turning the thermostat back 7° to 10°F for 8 hours a day can cut yearly heating and cooling costs by as much as 10%. A smart thermostat makes that happen without anyone remembering.
At $50 a year, a $130 thermostat pays for itself in about 2.5 years and a $280 one in 5 to 6. Many utilities offer rebates or bill credits for joining peak-demand programs, which shortens that.
The Features That Change Your Bill
- Automatic setbacks. Learning models build a schedule from your manual adjustments; others ask you to set one in the app. Both save energy, but learning helps households that never touch a schedule.
- Occupancy detection. Geofencing uses phone location to switch to away mode. Every adult must install the app and share location, or the house can cool down while someone is still home.
- Remote room sensors. These let the thermostat read the rooms you are using instead of the hallway. They matter in multi-story homes and add little in a one-zone apartment.
- ENERGY STAR certification. The criteria require low standby power, scheduling and monthly HVAC runtime reporting, so a certified model gives you the data to spot waste.
- Features that don’t cut runtime. Built-in speakers, air quality monitors and large displays can be useful, but they don’t lower the bill.
Check for a C Wire Before You Buy
Most Wi-Fi thermostats are built for 24-volt low-voltage systems and need steady power from a common, or C, wire. This five-minute look tells you which models fit before you spend anything.
- Turn off the furnace or air handler at the breaker; Google’s guidance is to cut power at the breaker before handling thermostat wires.
- Pull off the old thermostat face and photograph the terminals and their letters.
- Read the letters. A wire on C means any model fits; wires on O/B and AUX or W2 usually mean a heat pump, which narrows your shortlist.
- Stop if you see thick wires joined with wire nuts or a 120V or 240V label. That is line voltage, and standard smart thermostats won’t work on it.
No C wire? Nest models run without one in many systems, and Google sells a Nest Power Connector for those that don’t.
Ecobee includes its Power Extender Kit with the Smart Thermostat Premium and Enhanced, and Honeywell Home sells a C-Wire Power Adapter.
Adapters connect at the furnace control board, so factor that into your choice. Our smart thermostat installation walkthrough covers the wiring itself, or an HVAC technician can do it.
Current Models Compared by Published Specs
These five examples cover the main types. Prices are rounded US list prices from each maker; retail prices change often, and utility rebates frequently lower them.
| Model | List price | Scheduling style | Room sensor | Without a C wire | Platforms |
|---|---|---|---|---|---|
| Google Nest Learning Thermostat (4th gen, 2024) | About $280 | Learns from your adjustments | One Nest Temperature Sensor in the box | Works in many systems; Nest Power Connector sold separately | Google Home, Matter |
| Google Nest Thermostat (2020) | About $130 | Schedule you set, plus presence-based Eco mode | Not supported | Works in many systems; Nest Power Connector sold separately | Google Home, Matter |
| ecobee Smart Thermostat Premium | About $250 | Schedule plus occupancy sensing | One SmartSensor included | Power Extender Kit included | Apple Home, Alexa, Google Assistant |
| ecobee Smart Thermostat Enhanced | About $190 | Schedule plus occupancy sensing | Sold separately | Power Extender Kit included | Apple Home, Alexa, Google Assistant |
| Honeywell Home T9 | About $200 with one sensor | Schedule plus geofencing | One included; supports up to 20 | C-Wire Power Adapter; check kit contents | Alexa, Google Assistant |
The Nest Learning Thermostat 3rd generation from 2015 has been replaced by the 4th generation. If you are offered an older Nest secondhand, note that Google ended app support for the first and second generations in October 2025.
Apartments, Two-Stories, Heat Pumps and Baseboard Heat
One-zone apartment, empty on weekdays
In a one-bedroom apartment with a single gas furnace, geofencing plus a simple overnight schedule captures nearly all the savings. A basic model such as the Nest Thermostat or ecobee Enhanced is enough; sensors add little.
Renters should get written permission first, then bag and label the old thermostat and its screws for reinstalling at move-out.
Two-story house with a hot upstairs
When the thermostat sits in a first-floor hall of a two-story house, the downstairs often overheats while bedrooms stay cold. A sensor in the main bedroom lets the system hold that room at night instead of the hallway.
Someone home most of the day
Remote workers and retirees have little empty-house time, so geofencing and learning do less. Savings come mainly from overnight setbacks, which an inexpensive model with a good schedule handles well.
Heat pump homes
Confirm the model supports your heat pump wiring, including the reversing valve (O/B) and auxiliary heat. Deep setbacks can force a morning recovery on electric strip heat, which erases the savings, so use smaller setbacks.
Electric baseboard heat
Baseboard systems need line-voltage smart thermostats, a separate product category installed one per room. Because these carry 120 or 240 volts, hire a licensed electrician unless you are qualified for household wiring.
Setpoints That Capture the Savings
Start here, then adjust one or two degrees at a time over a week. Keeping setbacks consistent matters more than any single number.
| System and season | Home and awake | Asleep | Away 8+ hours |
|---|---|---|---|
| Furnace, heating | 68°F | 60–62°F | 60°F |
| Heat pump, heating | 68°F | 64–65°F | 64–65°F |
| Central AC, cooling | 78°F | 78–80°F | 82–85°F |
In freezing weather, don’t set heat below about 55°F while traveling; our guide to preventing frozen pipes covers the rest. Leave cooling lower if pets stay home in summer heat.
Use milder setbacks than the table suggests if an infant or older adult lives in the home.
Keeping the Thermostat Saving for Years
- Read the monthly runtime report. A jump in runtime during similar weather often points to a clogged filter or failing part; our HVAC maintenance guide lists what to check.
- Fix the house, not just the settings. Drafty rooms make any thermostat run longer, so pair it with insulation and air sealing.
- Keep sensors honest. Mount the thermostat and remote sensors away from direct sun, supply vents, kitchens and exterior doors, and replace sensor batteries when the app warns.
- Plan for software life. The hardware usually outlasts app support, so weigh each maker’s support history when spending more for a premium model.
A thermostat is one lever among several; our list of energy changes that pay for themselves ranks the others by payback.
