Smart Home

What is a smart thermostat and how does it work?

They regulate temperatures (obviously) but what makes them smart?

What is a smart thermostat and how does it work? Credit: Sensi

Recommendations are independently chosen by Reviewed’s editors. Purchases you make through our links may earn us a commission.

I’ve lived in New England for six years now, which means two things: I’ve learned to never call Tom Brady overrated, and I’ve learned the importance of having a thermostat that actually works. If you live in an old home or apartment like me, you likely have a bulky thermostat with supposedly programmable settings that mostly work, but don’t do much for actually regulating temperature reliably. Or you’ve got a clunky dial that allows you to manually change the temperature, but only when physically standing in front of it.

Naturally, there’s been a surge in the market for people hunting for better ways to control their home environment. If you’re looking for a sleek and easy way to upgrade your home’s temperature controls, you’ve likely already started researching smart thermostats. These devices are more expensive than standard thermostats, but they can make a world of difference in your home by helping you save on your energy bill and providing a more comfortable home environment tailored to your individual comfort.

Popular brands include Nest and Honeywell, but our testing found the Emerson Sensi Touch Wi-Fi Smart Thermostat to be the best smart thermostat available.

So what makes them smart? How are these home devices different from standard thermostats you can get for less than $20? We’ll dive into what makes a smart thermostat tick, what other devices in your home they’re compatible with, and whether you can install it yourself.

What is a smart thermostat?

Smart thermostat
Credit: Reviewed / Jackson Ruckar

Smart thermostats monitor and regulate your home’s temperature.

Just like the thermostat you’ve got now, a smart thermostat allows users to change the temperatures in their homes. Many come with touch screens that replace knobs and buttons, which provide a more user-friendly interface. Smart thermostats also come with mobile apps that allow you to remotely adjust settings, and they’re compatible with voice-controlled personal assistants, like Amazon Alexa and Google Assistant.

These smart home devices put user experience first, meaning they are built to be intuitive and easy to use, unlike the old thermostat in my first apartment that came with 14 buttons, one of which was permanently smashed in. They’re also intuitive, meaning they can learn your patterns and adjust heating settings to provide optimal energy saving in your home.

How does a smart thermostat work?

Smart thermostat
Credit: Reviewed / Julia MacDougall

Ignore the note; smart thermostats are meant to be touched.

Smart thermostats are wired into a home’s HVAC system, typically through what’s called a common wire, or C wire. Older homes may not have a C wire, meaning you can still get a smart thermostat, but you’ll need to have the house wired for a C wire first. This wire is integral for properly installing a smart thermostat, as it connects the device to your HVAC system without messing up wiring for the furnace or other appliances in the house.

Smart thermostats connect to your home’s WiFi, then allow you to access the device’s unique temperature settings, which may include:

Mobile control: Most smart thermostats have touch or digital screens that allow you to change temperatures, but they also come with mobile apps designed to allow users to control the home environment from the couch or the car. This is a great feature if you like coming home to the perfect temperature, or adjusting the settings without having to get out of bed. You can also use mobile apps to set programs or remotely monitor your home’s temperature while you’re out of town.

Smart thermostat app
Credit: Sensi

Mobile apps allow users to control their smart thermostat’s settings from the couch.


Humidity controls: My house does this really cool thing where some mornings all our windows get covered in moisture and we have to go around with towels to dry them off. Sounds fun, right? It’s not. But with a smart thermostat, we would at least be able to stay on top of it—you can’t actually adjust your home’s humidity, but you can monitor it and even set an alarm to go off on your phone if it changes.

Geofencing capability: Smart thermostats allow you to program your thermostat to run during particular times of the day, but what about those days when you want to break free of your routine? Geofencing allows you to go on an impromptu trip without stressing about your energy bills—using geotracking technology, some smart thermostats can register when you’ve left the house, then adjust the home’s temperature accordingly to ensure you are remaining efficient with your energy usage.

Connection to smart speakers: Our favorite smart devices are the ones that can speak to each other. Many thermostats can be paired with smart speakers you may already own—we compiled a list of all the best devices that are compatible with Amazon Echo and Google Home, and our top-rated choice, the Emerson Sensi Touch Wi-Fi Smart Thermostat, made both lists. But most smart thermostats should be compatible with at least one, if not all, top-selling smart speakers. If you’re unsure, consult the user manual that came with your thermostat.

Can I install a smart thermostat or does a professional need to?

Pro installing a smart thermostat
Credit: Spates / Getty Images

If you thought HVAC was a cool new trend among the youths, you need a professional to install your thermostat.

I don’t want to brag, but I installed the ground wire in my garbage disposal without any help (sorry men, I’m taken). But would I trust myself to take out my old thermostat that’s likely older than I am, rewire my house with a C wire, then install a smart thermostat? Absolutely not. And if you’ve already forgotten what a C wire is, you should probably hire a professional, too.

This really comes down to your familiarity with HVAC systems, comfort level around electrical wires, and ability to easily follow the directions that come along with the thermostat. Personally, I would start by removing my old thermostat and finding out whether my house has a C wire—many smart thermostats say they can operate without a C wire, but the connection would not be optimal. Essentially, this means your thermostat may run, but its WiFi connectivity and power connection may not be fully stable, both of which are about the opposite of what you want with any smart device.

If I could easily find and identify the C wire (which should be labeled as such), I would likely install a smart thermostat on my own. But I live in a fixer-upper and I’ve had my share of installing my own appliances, including my dishwasher and garbage disposal. Plus, my father is a handyman who went to school for electrical wiring, so I feel confident he could coach me through it.

But if my house didn’t have a C wire? I would absolutely hire a professional to come out and install it. And if I didn’t already have experience with installing appliances on my own, paying $150–$200 for a professional to install it for me would be worth the peace of mind. They’d likely also be helpful in identifying the best place to install your thermostat to ensure you’re getting optimal benefits.

It’s incredibly hard and expensive to fix faulty wiring, so if you don’t know what you’re doing, call the pros.

Is buying a smart thermostat worth it?

Smart thermostat in home
Credit: Sensi

Smart thermostats are great investments for those looking to cut energy costs.

There are lots of benefits to owning a smart thermostat, but are there enough to justify their cost, as well as the potential cost of installation?

Ideally, a smart thermostat should pay for itself after a year or two with the money you save in energy costs. Since the thermostat can track when you’re home and when you need the most heating, it can ensure efficiency in your home and prevent unnecessary spending on heat. Plus, these energy-efficient appliances are good for the environment, meaning you may be eligible for a rebate for simply owning one.

If you’re a homeowner, the temptation to purchase a smart thermostat may be greater than if you’re a renter. Can you even install a smart thermostat in an apartment? It depends on if you can find one that doesn’t operate with a C wire or one that your landlord will approve.

Overall, if your current thermostat is on its way out, it’s probably worth upgrading to a smart thermostat that can live in your house for the next 20–30 years and provide you with a variety of benefits that can improve your quality of living. If your thermostat works perfectly fine, a smart thermostat may be a good investment if energy efficiency is at the forefront of your mind. For the best smart thermostat you can buy, we recommend the Emerson Sensi Touch Wi-fi Thermostat, which you can get on Amazon for $143.97. Our favorite affordable pick is the Emerson Sensi Wi-fi Thermostat, which you can get on Amazon for about $100.

The product experts at Reviewed have all your shopping needs covered. Follow Reviewed on Facebook, Twitter, and Instagram for the latest deals, product reviews, and more.

Prices were accurate at the time this article was published but may change over time.

Up next

View all Home & Outdoors