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Smart thermostat buying guide

Considering a heating and cooling upgrade? Here's everything you need to know about smart thermostats.


While heating and cooling setups can vary a lot, most US homes rely on some sort of heating, ventilating and air conditioning system (HVAC) to help keep indoor temperatures in check. Your thermostat acts as the main point of access for this system, allowing you to determine when and at what temperature air is circulated. The thing is, today's thermostats are quite different than the typical models sold in stores just 10 years ago.

That's where this buying guide comes in handy. We'll explore the changing thermostat market, so you can decide which model makes the most sense for your home.

There are plenty of other products that can help regulate your home's temperature, like Big Ass Fans' Haiku Ceiling Fan with SenseMe and Lutron's Serena Shades, but we're focusing on stuff that directly interacts with HVAC systems here. We'll also take a quick look at supplemental HVAC devices like smart vents, which promise to work in tandem with your thermostat to deliver an unprecedented level of control over each room.

Basic thermostats

Programmable thermostats are pretty common nowadays. To configure them, you simply enter in a general schedule that's consistent with the times you expect to be home or away.

If you work a traditional 9-to-5 job, this sort of thermostat can work quite well. Simply set the thermostat to a more energy efficient temperature while you're at work and program it to kick back on around the time you usually get home. That way, you have one setting for the weekdays and another setting for the weekends. And of course, you can always make manual adjustments to the thermostat as needed.

A typical programmable thermostat.

Chris Monroe/CNET

While programmable thermostats do count as a type of automation, they aren't exactly smart.

That's because they don't have the ability to automatically adapt to your changing schedule; you still have to make adjustments manually if you want to tweak the existing programming settings.

In contrast, smart models like the Nest Learning Thermostat, the Honeywell Lyric T5 and the Ecobee3 are trying to give you greater control over your heating and cooling environment with Wi-Fi integration, web and mobile apps and even sensors that can tell if you're home.

All of the above models are DIY options. That means that you don't have to get in touch with a dealer unless you want to. Instead, you can find these models alongside the more traditional manual and programmable options in most major retails stores. That makes these smart versions a fairly easy upgrade.

Smart thermostats

Of the models we've reviewed so far, we've seen three main types of smart thermostat tech: learning algorithms, geofencing and motion sensors.

  • Algorithms

The Nest Learning Thermostat, the Honeywell Wi-Fi Smart Thermostat and the Honeywell Wi-Fi Smart Thermostat with Voice Control all rely on algorithmic-based learning. With these three thermostats, you can input the basic parameters for your schedule, similar to a traditional programmable model, but they also have the ability to learn your schedule over time and adapt automatically to changing patterns.

For instance, the Nest has an Auto Away feature. If you don't pass in range of its 150-degree motion and light sensors for a while, it will assume that you're gone (even if it's during a time that you're supposed to be home) and default to the more energy efficient Away mode. And, if your Nest starts to "notice" that you're regularly gone during this time, it will start to learn this new pattern in your routine and adjust its schedule accordingly.

Of course, this isn't perfect. It could be that you're home sick and haven't walked in front of the thermostat all day because you're resting in bed. Then, you might find that you'll need to make a quick manual adjustment on the app or on the thermostat itself just to let it know that you are in fact home.

  • Geofencing

The Honeywell Lyric app.

Screenshot by CNET

Unlike the Nest Learning Thermostat and two of Honeywell's other smart models, the Honeywell Lyric and Lyric T5 rely on your phone's geofencing feature to tell whether you're home or away. You can set the range to either 500 feet or 7 miles so that when you get outside of that 500-foot or 7-mile range, your thermostat should automatically set to Away mode. And, when you cross back under that threshold, it's supposed to return to Home mode so it's nice and cozy when you arrive.

This is a clever idea, assuming that you don't regularly forget your phone at home, but it doesn't always work well in practice. Imagine having multiple family members with the Lyric app and the geofencing feature enabled -- that could create a lot of headaches. And, if you work near home, you might inadvertently trigger Home mode as you go about your daily routine.

  • Remote sensor

Somewhat similar to the Honeywell Lyric thermostat, the Ecobee3 thermostat relies on motion and proximity sensors. Its sensors will detect that you're near and kick into home mode. If it senses that you've been gone for a while, it will switch to away mode. This worked well, especially because it relied on a remote sensor. Placing the remote sensor in a heavily trafficked part of the house helps ensure that its Home and Away mode is accurate.


The Ecobee3's remote sensor.

Ry Crist/CNET

Of course, this tech is entirely dependent on you walking around and triggering the sensors. If you don't happen to cross within range of the sensors, the Ecobee3 will assume you're out.


If you've installed a four- or five-wire thermostat before, this process should be roughly the same. The only thing you need to keep in mind is that some of the thermostats will require a C wire and some won't. When in doubt, ask a professional or qualified friend for help. Typically, though, it shouldn't take too long to get any of these smart thermostats successfully connected to your HVAC wiring.

The C wire, also called the "common" wire, is required for the Honeywell Wi-Fi Smart Thermostat, the Honeywell Wi-Fi Smart Thermostat with Voice Control, the Ecobee3 and the Ecobee3 Lite. This wire provides a continuous flow of power (24 VAC, to be exact) so that fancier features, like LED displays function properly.

The Nest Learning Thermostat and the Honeywell Lyric are compatible with four-wire setups in some cases (again, ask a professional if you're unsure). That's because other wires, particularly the R wire, can supply enough power to do the C wire's job. There is controversy surrounding this method, though. It's commonly referred to as "power stealing," as it borrows power from other wires to account for the missing C wire. (Find out more about the C wire here.)

One key benefit of four-wire compatibility is that you don't have to rewire your HVAC with a C wire to get smart thermostat functionality, but it is a bit of a "workaround" that could potentially harm some systems.

App talk

Configuration will vary based on the specific product, but each smart thermostat will ask you a variety of questions, such as what type of system you have, what fuel source you use, whether you have one- or two-stage heating and cooling and so on.


Setting up the Honeywell Lyric.

Screenshots by Megan Wollerton/CNET

This is also where you'll be able to set some basic minimum and maximum preferred temperatures as well as what type of alerts, if any, you'd like to receive. After that, you're ready to start controlling your thermostat remotely, a great feature for those times when you want to set it to Vacation mode from the road or simply make small tweaks from the comfort of your couch.

heat type setup

What type of system does your home use?

Lindsey Turrentine/CNET


Apple alums Tony Fadell and Matt Rogers took a major design leap with the rounded Nest Learning Thermostat. Most of the thermostats in stores look pretty utilitarian. That standard plastic white finish has a purpose, though; it's supposed to blend into any environment.

But Fadell and Rogers made their thermostat something that you'd actually want to look at. The Honeywell Lyric, Lyric T5, Ecobee3 and Ecobee3 Lite followed suit with designs that depart from the traditional aesthetic. So, if you're in the market for something with advanced functionality that also looks neat, one of these models is a solid bet.

Is it worth it to go smart?

With HomeKit, you can ask Siri to control your heating and cooling.

Tyler Lizenby/CNET

Smart thermostats are increasingly becoming a part of the larger smart home landscape. The "Works with Nest" initiative makes it possible for folks to integrate the Nest Learning Thermostat, the Nest Protect and Nest security cameras with a variety of third-party products, ranging from Whirlpool to Lutron. Nest, Ecobee and Honeywell also have their own IFTTT channels for more advanced home automation rules.

Additionally, all three brands work with Amazon Alexa. That means you can adjust your thermostat with a simple voice command: "Set my thermostat to 68," "What's the current temperature of my thermostat?"
and so on. Ecobee3 and Honeywell Lyric thermostats also work with Apple HomeKit, so iPhone customers can adjust their thermostat with Siri. Nest's thermostat is the first to work with the Google Home for custom commands like, "OK Google, raise the temperature to 72."

But smart thermostats don't come cheap. You can snag a basic 7-day programmable thermostat for less than 30 bucks, while these smart models range in price from $150 to $250 (at the current exchange rate, that's about £120, AU$200 to £200, AU$330). So, even if you're saving money on your energy bill, it might take awhile for the upfront cost to even out.

Beyond thermostats

There are a few DIY smart vents that promise to bring even more energy savings your way: Ecovent, Linq and Keen. The idea is that you would replace all of the vents in your home with smart versions. They all use ambient sensors to get the actual temperature readings by room so you can make adjustments accordingly. You can also use them to route your heating and cooling only to the room that you're currently occupying. This sounds pretty neat, but the ones we've tested so far fell far short of our expectations.


Keen Home Smart Vent styles.

Sarah Tew/CNET

Is a smart thermostat for you?

Heating and cooling plays a huge role in your connected home. It keeps you cozy, but there's a definite balance between comfort and saving money. While traditional thermostats can certainly do the job, the next generation of home heating and cooling devices are trying to give you even more control over your environment.

In the end, though, it's all about what makes sense for you. Compare the options out there to your needs and then decide if a smart thermostat is a worthwhile upgrade.