Smart Thermostats Explained: How They Reduce Heating and Cooling Use
How smart thermostats work, how much energy they can save, and what to check for compatibility before you buy.
In this guide
Key takeaways
- ENERGY STAR says certified smart thermostats save about 8% on heating and cooling bills on average.
- Savings come from turning heating and cooling down when you're asleep or away.
- Check compatibility with your system, including whether you have a C-wire.
- Many utilities offer rebates on smart thermostats.
Introduction
Heating and cooling make up a large share of most home energy bills. A smart thermostat helps by adjusting the temperature automatically when you're asleep or away, without you having to remember.
This guide explains how they work, what savings to expect and what to check before you buy one.
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What makes a thermostat "smart"
A smart thermostat connects to Wi-Fi and can be controlled from your phone. Most also offer some of these features:
- Learning: some learn your routine and build a schedule automatically.
- Occupancy and geofencing: they can sense when nobody's home, or use your phone's location to change the temperature as you leave or return.
- Energy reports: they show how much your system runs and how settings affect it.
- Alerts: notifications for problems, such as a reminder to change your filter or an unusual temperature.
A programmable thermostat can follow a schedule too, but it only works if you set it up. ENERGY STAR notes that many people never program theirs.
How much can you save?
ENERGY STAR says certified smart thermostats save about 8% on heating and cooling bills on average, or about $50 a year. Savings can be higher in homes with high heating and cooling bills, and lower in mild climates or homes that are almost always occupied.
The principle behind the savings is simple. The US Department of Energy says 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 does this for you automatically.
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Not now, show me another guide →Check compatibility before you buy
Most smart thermostats work with common systems, but it's worth checking first:
- Your system type: gas or oil furnace, heat pump, central air, boiler or a combination. Most manufacturers have an online compatibility checker.
- The C-wire: many smart thermostats need a "common" wire for constant power. Take a photo of the wires behind your current thermostat before you shop. Some models include an adapter if you don't have one.
- High-voltage systems: electric baseboard heaters usually need a special line-voltage thermostat. A standard smart thermostat won't work with them.
- Heat pumps: choose a model designed for heat pumps, so setbacks don't trigger expensive backup heat.
Installing a smart thermostat
Many people install a smart thermostat themselves in under an hour. The basic steps are:
- Turn off power to your heating and cooling system at the breaker.
- Remove the old thermostat cover and photograph the wiring and labels.
- Label each wire using the stickers that usually come in the box.
- Disconnect the wires and remove the old base plate.
- Mount the new base, connect the wires as shown in the instructions, and attach the thermostat.
- Restore power and follow the setup steps in the app.
If the wiring doesn't match the instructions, or you're unsure, an HVAC technician or electrician can install it.
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Settings that save the most
- Use setbacks: lower the heat or raise the cooling while you're asleep or away.
- Turn on away mode or geofencing, so the system eases off when everyone leaves.
- Avoid big swings: setting the temperature much higher or lower doesn't heat or cool your home any faster.
- Use a ceiling fan in summer. The Department of Energy says a ceiling fan can let you raise the thermostat about 4°F without losing comfort.
Rebates and the ENERGY STAR label
Many utilities offer rebates or bill credits for ENERGY STAR certified smart thermostats. Some also run demand response programs, where they make small adjustments during peak times in exchange for a credit.
The ENERGY STAR label means the model has shown energy savings based on real-world data from homes across the US. Check your utility's website for current offers before you buy.
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Smart vs programmable thermostats
| Programmable | Smart | |
|---|---|---|
| Schedule | Set by hand on the unit | Set in an app, or learned automatically |
| Remote control | No | Yes, from your phone |
| Knows when you're away | No | Often, using sensors or your phone's location |
| Energy reports | Rarely | Usually |
| Needs Wi-Fi | No | Yes, for most features |
If you already have a programmable thermostat and use its schedule well, you may already be getting much of the saving. A smart model makes it easier to keep doing it.
Privacy and security
Smart thermostats collect information about when you're home. Before you set one up, check the manufacturer's privacy settings, use a strong unique password, turn on two-factor sign-in if it's offered and keep the device's software updated.
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Conclusion
A smart thermostat won't change your heating and cooling system, but it can help it run less when nobody needs it. Check compatibility first, look for the ENERGY STAR label, use setbacks and away settings, and check your utility for a rebate.
Common questions
Do smart thermostats work without Wi-Fi?
They usually keep running your schedule without Wi-Fi, but you lose remote control, app features and updates until the connection returns.
What is a C-wire?
It's a "common" wire that provides constant power to the thermostat. Many smart thermostats need one, though some include an adapter.
Can renters use a smart thermostat?
Often, with the landlord's permission. Keep the old thermostat so you can reinstall it when you move out.
Sources and further reading
This guide is general information. Follow the manufacturer's instructions and local rules, and use a licensed professional for electrical work you're not comfortable doing.
