What to know before installing a smart thermostat

So-called smart thermostats are becoming more and more common. While there is no consensus on what exactly makes a thermostat "smart," homeowners should look for two key features.

First, smart thermostats contain programming capabilities that go above and beyond the simple time-and-temp programming features found in the programmable thermostats of yore. Second, smart thermostats should be able to connect to your home's Wi-Fi.

Why is Wi-Fi important? Having a connected device means you can control your home's temperature using a smartphone app or using a virtual assistant like Apple's Siri of Amazon's Alexis. This is a definite plus when your thermostat is on a different floor or on the far side of your home, or if you're traveling and remember that you forgot to adjust the temperature before leaving.

"I love Wi-Fi thermostats," Steve Lauten, president of Total Air & Heat Company in Plano, Texas, says. "Basically a Wi-Fi thermostat gives you the ability to change the temperature in your house anywhere in the world. More advanced ones will even show you how much energy you're using, and can be set to go into energy-saving mode in periods of peak demand."

A recent article on The Wirecutter, a website that tests and recommends the latest gadgets, took a look at the top smart thermostats on the market today.

Their top pick was the Nest Learning Thermostat, on the market for about $250 from most retailers. As the original smart thermostat, Nest's offering has the advantage of being on the market the longest. The Wirecutter's reviewers note that it had the easiest, sleekest user interface, and that its "learning capabilities make the Nest the smartest smart thermostat around."

The Nest will learn your home HVAC habits and even has sensors to see if you or your family is at home. Over a period of a few weeks, it will gradually create its own schedule of heating or cooling for maximum comfort.

Coming in second place is the Ecobee3. One advantage of the Ecobee is that it comes with extra sensors, which can be placed in hot or cold spots in your home. This is especially helpful if you have a large home or a weak HVAC system. The Ecobee also integrates with Amazon's Alexa home assistant and Apple's Siri.

As a budget pick, The Wirecutter recommends the Emerson Sensi thermostat. It doesn't have as many frills as the others, but it can run on AA batteries, unlike the Nest or Ecobee. (More on that in a moment.) And for those on a tight budget, the Sensi costs about half as much as the other picks.

"Homeowners certainly need to keep in mind what type of system they have," Lauten says. "How you wire the thermostat is different depending if you're all electric or have a gas system. I'd recommend taking a picture of the wiring before starting, so that you make sure to wire it up the same way."

Manufacturers include installation instructions for DIYers to consult. "Of course, we do get service calls because people install them wrong," Lauten says. He recommends that homeowners unsure about how to properly install their new smart thermostat contact a reputable HVAC contractor.

Both Nest and Ecobee recommend that your home have what's called a C-wire - a dedicated electric line that supplies enough juice to support the thermostats' power-hungry Wi-Fi functions. Depending on the age of your system, you might also need to have a contractor install the appropriate wiring.

Most HVAC manufacturers offer their own Wi-Fi thermostats that are specifically paired with their equipment. These make sense if you're having a complete system installed, according to Francis Dietz, vice president of public affairs at the Air-Conditioning, Heating and Refrigeration Institute.

Dietz adds that even if homeowners aren't ready to invest in a smart thermostat, even a programmable thermostat offers some benefits. "These models can save homeowners money because they automatically adjust the temperature based on a homeowner's input depending on when the home will be occupied," he says, "eliminating the possibility of forgetting to set it properly. These devices also will remember the daytime or nighttime temperatures from season to season, so the homeowner does not have to."