How popular are smart thermostats these days? Consider this: The Nest thermostat, that futuristic-looking, Apple-designed device we wrote about last month, has been so hot they’ve been on back-order. Thermostats!

Well, now the state-of-the-art home-energy-management-system field is getting even more interesting. Comcast, the nation’s largest cable provider, announced last week that it’s adding home energy management to its portfolio. Yes, that’s right: Smart HVAC companies like Nest, ecobee, and Lutron are being joined by cable-and-Internet heavyweights.

It’s a big move into a burgeoning market for Comcast. Last week’s news was highlighted by a partnership with EcoFactor, which sells an automated energy-management service. Not all the details of the deal have been announced yet, but basically, EcoFactor, which has been building out its technology for several years, will provide its smart energy management services to Comcast customers as part of its Xfinity Home package.

Comcast will conduct all the training and installations associated with the new offering, and management will be handled through the Xfinity Home platform.

What’s interesting about this deal is that EcoFactor doesn’t actually make thermostats. Though there are some similarities to the capabilities of the Nest thermostat, EcoFactor has developed a cloud-based software that can plug into any web-connected thermostat to optimize HVAC efficiency, which typically accounts for about 50 percent of home energy costs.

Both systems use Internet connections to make automatic temperature adjustments based on weather conditions, and both can “learn” their owners’ behavior to optimize and lower energy use. But EcoFactor has more predictive bells and whistles than Nest, including analyzing weather patterns and the structure of the house, so the system is more fully automated.

EcoFactor users have seen HVAC costs reduced by up to 30 percent. When we talked to Nest last month, they hadn’t done any studies yet to determine actual savings.

EcoFactor has inked deals with other large companies in the past two years. In 2010 it agreed to provide Oncor, a Texas utility company, with its service, and in 2011 Nevada’s NV Energy signed on as well. Comcast, for it’s part, has been pushing into markets outside its cable/Internet bread-and-butter since it started offering home security services over a year ago.

Until now, smaller independent vendors have largely dominated the growing smart thermostat market by selling directly to consumers. But now the big boys want in. Fellow telcos Verizon and Time Warner have both launched home energy management services, connecting end-users with smart thermostats, however both offerings lack the automation capabilities of the Comcast/EcoFactor solution.

Nevertheless, the entrance of these kinds of companies in the smart home energy management fray shows how popular, lucrative, and important the industry is becoming. Who knows what part of your life they’ll want to get into next!

Click here for a video of Comcast’s Mitch Bowling explaining the news.