Those little boxes that usher cable signals and digital recording capacity into televisions have become the single largest electricity drain in many American homes, with some typical home entertainment configurations eating more power than a new refrigerator and even some central air-conditioning systems.

There are 160 million so-called set-top boxes in the United States, one for every two people, and that number is rising. Many homes now have one or more basic cable boxes as well as add-on DVRs, or digital video recorders, which use 40 percent more power than the set-top box.

One high-definition DVR and one high-definition cable box use an average of 446 kilowatt hours a year, about 10 percent more than a 21-cubic-foot energy-efficient refrigerator, a recent study found.

These set-top boxes are energy hogs mostly because their drives, tuners and other components are generally running full tilt, or nearly so, 24 hours a day, even when not in active use. The recent study, by the Natural Resources Defense Council, concluded that the boxes consumed $3 billion in electricity per year in the United States — and that 66 percent of that power is wasted when no one is watching and shows are not being recorded. That is more power than the state of Maryland uses over 12 months.