Of all the energy-saving devices in your home, the thermostat has the most potential to save you money.

Yet for years, programmable thermostats weren’t eligible for Energy Star certification—the badge of honor for energy misers—because they were so complicated that homeowners weren't taking advantage of their capabilities. They're still a pain, but the new category of WiFi-connected smart thermostats are now eligible, and this week the Nest became the first smart thermostat to be certified by Energy Star.

"We know that our thermostat helps people save energy, and now the EPA Energy Star program wants everyone to know it too," said Ben Bixby, director of energy business at Nest Labs, which is owned by Google's parent, Alphabet.

Actually, it wasn’t that simple.

In 2009, the Energy Star specifications for programmable thermostats were suspended because most of the devices were too confusing to program and even people who installed them didn’t use them properly. Those findings were borne out in Consumer Reports' ease of use tests for programmable thermostats, which showed that many of the early generation models were far from intuitive.

So while manufacturers got busy making thermostats that were more consumer friendly, the Environmental Protection Agency (EPA) set about rewriting its Energy Star specifications for thermostats based on real homeowner data. The result is new specs for WiFi-enabled smart thermostats that took effect January 1.

"Anyone who cares about energy savings but is too busy to think about their heating and cooling use can be assured that these products have shown they help other busy families," said Abi Daken, program manager for Energy Star HVAC products.

Invented by former Apple engineers, the Nest got a lot of buzz when it was introduced in 2011. Consumer Reports tested an earlier generation of the Nest—the company is now on its third gen model—and it wasn’t the top performer in our tests. But it can surely be credited as the product that raised the profile for the entire category.

Energy Star defines smart thermostats as WiFi-enabled devices that automatically adjust heating and cooling temperature settings for optimal performance. Typically they have features that "learn" the temperatures you prefer and help you set a schedule that reverts to energy-saving settings when you’re asleep, away, or at work. They can be controlled by your smartphone and also provide data so you can track your energy use and act accordingly.

Energy Star says that the energy savings can add up quickly. On average, a homeowner using a certified smart thermostat will save more than 8 percent of their heating and cooling energy, amounting to at least $50 a year.

At Consumer Reports, we’re in the process of buying and testing a new batch of thermostats including the most recent Nest as well as the latest models from ecobee, Honeywell and other manufacturers. In our thermostat tests, we look past the coolness factor to focus on whether a thermostat works well enough to actually keep you cool.