In this section
- CalculatorSetback calculatorHow much does turning the thermostat down at night and while you're out save? Uses the Department of Energy's rule of thumb.
- GuideC-wire guideWhat a C-wire is, how to check if you have one, and your options if you don't: an adapter, a spare wire, or a thermostat that doesn't need one.
What they actually save
ENERGY STAR measured certified smart thermostats in real homes and found average savings of about 8% on heating and cooling bills, around $50 a year; homes with high bills can save up to about $100. The Department of Energy says setting the thermostat back 7 to 10°F for 8 hours a day can save up to 10% a year. A smart thermostat’s job is to do that automatically, every day.
Before you buy
- C-wire. Most smart thermostats need constant 24 V power from a common wire. How to check.
- Heat pumps. Choose a thermostat that supports heat pumps and set it up for your system. DOE warns against deep setbacks on a heat pump without a thermostat designed for it, because a big recovery can switch on the expensive backup heat strips.
- Electric baseboards need a line-voltage thermostat, not a standard smart thermostat.
- Old Nest owners: Google ended app support for the 1st and 2nd generation Nest Learning Thermostats on Oct 25, 2025. They still work as basic thermostats, but no app, schedules from your phone, or Home/Away.
Ask your utility
Many utilities give rebates for ENERGY STAR certified smart thermostats, and some pay you to enroll in a program that nudges the temperature during peak demand. Both can cover much of the cost.
Picks
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Google Nest Learning Thermostat (4th gen)
Set-and-forget learning schedules
- Includes a Nest Temperature Sensor
- Works with Google Home
Learns your schedule and turns itself down when the house is empty.
Watch for: 1st and 2nd gen Nest Learning thermostats lost app support on Oct 25, 2025. This one replaces them.
ecobee Smart Thermostat Premium
Homes with hot and cold rooms
- Comes with a SmartSensor for another room
- Built-in air quality monitor
Room sensors let it heat the rooms you're actually in, not just the hallway.
Watch for: Needs a C-wire or ecobee's power adapter.
Amazon Smart Thermostat
Cheapest ENERGY STAR smart thermostat
- ENERGY STAR certified
- Works with Alexa
Gets you schedules and remote control for the least money.
Watch for: Requires a C-wire; buy the C-wire adapter if you don't have one.
Honeywell Home T9
Room sensors at a lower price
- Supports multiple room sensors
- Works with major assistants
Averages or prioritizes rooms, like ecobee, for less.
Watch for: Needs a C-wire.
Sensi Smart Thermostat (ST55)
Homes without a C-wire
- Sensi says many systems don't need a C-wire
- Wi-Fi app with schedules
Avoids adding a wire or adapter on many older systems.
Watch for: Check Sensi's compatibility tool for your system first.
Mysa smart thermostat for electric baseboards
Apartments with electric baseboard heat
- Line-voltage (120/240 V) thermostat
- Schedules and energy reports
Baseboard heat is expensive; schedules per room cut it.
Watch for: Line-voltage wiring can injure you. If you're not sure, hire an electrician.