What Is a Smart Thermostat?

If you're trying to lower your heating and cooling costs, you might have tried improving your home's insulation or adding weatherstripping around leaky windows. 

If you're still feeling the pinch when it's time to pay your utility bills, it might be time to upgrade your thermostat. 

A Wi-Fi-enabled smart thermostat can be programmed from your smartphone, takes daily weather changes into account and even learns your household's habits to make your home more comfortable year-round. Plus, it helps you save money on heating and cooling.

Best Smart Thermostats of 2024 See at CNET

What is a smart thermostat?

A smart thermostat connects to your Wi-Fi, using the internet and other features to optimize your HVAC system's performance automatically. 

"A smart thermostat gives you visibility over your heating and cooling system," said Ross Trethewey, founder and lead engineer of TE2 Engineering and a building engineer on the television shows This Old House and Ask This Old House.

These web-enabled devices can offer convenience and optimization far beyond a standard thermostat. Motion sensors signal a smart thermostat to turn on when you walk in the door after work, while some models include remote sensors to ensure that different areas of your house are at the proper temperature. Access to local weather data and predictive analytics through Wi-Fi allow the system to adjust based on the conditions around your home before you start to sweat or feel a chill. 

Some smart thermostats can even be set to kick on when you're within a certain distance of your home so it's properly heated or cooled once you walk in the door. 

"With geofencing, you can pair your thermostat to your phone or multiple phones in the household," Trethewey said. "The thermostat uses the location of that cell phone to figure out whether you're in the range where it should keep the house comfortable." 

Smart thermostats vs. standard thermostats

A standard thermostat is pretty simple: It tells your heater or air conditioner when to turn on and off, and that's about it. With these older models, you turn a knob to set your desired temperature. The system runs until that temperature has been achieved, then shuts off again.  

"With the old systems, it's like you're either going 100 miles an hour or slamming the brake. There's no cruise control," Trethewey said. "A smart thermostat will turn your HVAC system on and off effectively to try to cruise control as much as it possibly can."

Standard thermostats must be adjusted manually. With a smart thermostat, you can control your HVAC system remotely with a swipe of your finger. 

"Because it's connected to an app on your phone, no matter where you are in the world, you can see the temperature in your house and adjust it," Trethewey said. "That creates huge convenience and peace of mind." 

What is a programmable thermostat?

A programmable thermostat is a little more customizable than a standard thermostat. You can pop off the cover and manually program this type of thermostat to kick on the heating or cooling and off at certain times based on the day of the week. That programming requires regular updates, assuming you took the time to figure out how to program it in the first place.

"Programmable thermostats can be incredibly complicated to set up and program properly, and then your schedule changes, so nobody programs their old-school thermostats," Trethewey said. "Smart thermostats can schedule themselves, and you can adjust that schedule very easily from the app on your phone, tablet or laptop."

Can a smart thermostat lower energy costs?

All those features add up to a more comfortable home, lower energy use and lower utility bills. "A smart thermostat can save anywhere from 5% to 15% on a homeowner's typical energy bill, around 8% on average," Trethewey said. Taking advantage of more of a smart thermostat's features generally correlates with more savings. 

Homeowners in regions of the US where utilities offer varying electric rates can save even more with a smart thermostat.

"If you live in a part of the country that has varying electric rates, there are smart thermostats that can use those time-of-use rates to get you even further energy savings," Trethewey said. "If your thermostat knows that the cost of electricity is going to escalate at two in the afternoon, it'll cool your house up to that time, then shut off and go into coast mode so you don't have to pay that higher rate for electricity."

A smart thermostat can go a long way to making your home greener and reducing your energy costs, but it's just one of a constellation of factors that affect your home's energy efficiency. 

"You're still limited by the air leakage, the insulation in the building shell, and the performance of your HVAC system," he said. Taking steps to improve the overall energy efficiency of your home through insulation and sealing gaps where air can escape will help increase your savings even more. 

Before you make the choice to upgrade to a smart thermostat, it's important to note that the technology is compatible with many (but not all) HVAC systems and equipment. In addition to making sure you have a strong Wi-Fi connection, you'll want to check that your HVAC equipment and wiring are compatible with smart thermostats. 

For example, those old-school standard thermostats with a dial, known as millivolt systems, may not be an easy swap with a smart thermostat because of their wiring. High-voltage electric baseboard heaters are often not compatible with smart thermostats. Mini-splits may be on communicating systems, which run via their own proprietary controls.

The best way to find a smart thermostat that's compatible with your HVAC system is to check the brand of your current equipment, seek out a smart thermostat from the same brand. Many manufacturers also offer third-party thermostat integration kits that can adapt an incompatible thermostat to work with their system. 

You can reach out to the manufacturer for guidance on which smart thermostat is compatible if you'd like to DIY. Otherwise, it's best to seek out a professional who works with your brand of equipment to get their recommendation for a smart thermostat that will work for your system as well as a professional install. 

"If you're driving a Volkswagen, you wouldn't bring it to a Chevy dealership to get serviced," Trethewey said. "If you have a certain brand of HVAC system, make sure to hire a company that specializes in that system."