HVAC buying guide

Considering a heating and cooling upgrade? Check out the growing variety of DIY smart-home options here.

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Heating and cooling setups can vary a lot, but 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 Jewell clock and thermostat, by the Electric Heat Regulator Co. eBay

The thing is, thermostats have changed significantly since they were invented in the late 1800s. A quick glance at one of the Electric Heat Regulator Co.'s (later known as Honeywell) earlier creations -- a clock-thermostat hybrid called the Jewell -- will confirm that. You'll find that there are many more options to choose from today, although none of them have quite as much character as the Jewell.

That's where this guide can come in handy. If you currently have a manual-control or a programmable thermostat, new smart options are quickly emerging in the DIY market that offer greater customizability so you can improve your comfort while saving money. We'll explore that growing smart thermostat landscape here, so you can decide if any of the products make sense for you. Plus, we'll take a look at some intriguing smart vent concepts that promise to work in tandem with your thermostat to deliver an unprecedented level of control over each room.

Of course, there are plenty of other products that can affect your home's temperature control, like Big Ass Fans' Haiku Ceiling Fan with SenseMe and the Quirky+GE Aros Smart Air Conditioner , but we're focusing on stuff that directly interacts with HVAC systems here.

Looking beyond the programmable thermostat

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. Home Depot

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.

Now, DIY models like the Nest Learning Thermostat , Honeywell Wi-Fi Smart Thermostat , Honeywell Wi-Fi Smart Thermostat with Voice Control , Honeywell Lyric and Ecobee3 are all trying to give you even 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 option.

Specific smart thermostat tech

Of the models we've reviewed so far, we have 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 Megan Wollerton/CNET

Unlike the Nest Learning Thermostat and two of Honeywell's other smart models, the Honeywell Lyric relies 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 that 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 didn't work particularly 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 model 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 accuracy is on point.

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, then the Ecobee3 will assume that 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.

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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 and the Ecobee3. 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.

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.

Configuration and using the app

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.

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 decided to make their thermostat something that you'd want to look at. The Honeywell Lyric and Ecobee3 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 three models is a solid bet.

Is it worth it to go smart?

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 and the Nest Protect with a variety of third-party products, ranging from Mercedes-Benz to the Dropcam Pro. The Nest thermostat also has its own IFTTT channel for more advanced home automation rules.

Ecobee integrates with SmartThings and Ubi and has its own IFTTT channel. Honeywell has a couple of IFTTT channels, although neither of them currently work with the Wi-Fi Smart, Wi-Fi Smart with Voice Control or the Lyric.

Given these integrations, smart thermostats (particularly the Nest) make sense for someone interested in diving into other home automation offerings.

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 $249 to $349 (at the current exchange rate, that's about £165, AU$325 to £230, AU$460). So, even if you're saving money on your energy bill, it might take awhile for the upfront cost to even out.

On the horizon

There are a few DIY concepts that promise to bring even more energy savings your way. Ecovent , Linq and Keen are smart vent concepts. 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 none of these products have hit retail yet.

Keen Home Smart Vent styles. Sarah Tew/CNET

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, it's nice to see that the next generation of home heating and cooling options are trying to give you even more flexibility 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.