One development that makes the high price of communicating thermostats more palatable is the trend toward "time-of-use" energy pricing. Some utilities now vary what they charge for electricity throughout the day, based on fluctuations in the demand for power. For instance, Gulf Power Company, which supplies electricity to 370,000 customers in Florida's panhandle, may charge 29 cents per kilowatt-hour on a hot August afternoon, and only 3.5 cents per kilowatt-hour during off-peak hours (9 p.m. to 6 a.m.). Homeowners who subscribe to Gulf's time-of-use pricing program for $4.53 a month are equipped with thermostats that receive a wireless signal from the utility. When the price of electricity is going to peak, the thermostat responds by automatically turning up the A/C temperature (by an amount predetermined by the homeowner) and turning off up to two other noncritical appliances (such as a water heater or a pool pump). The customer reaps the benefits in lower electricity bills. (Setbacks can be overridden manually, if need be.)

This thermostat also displays when peak rates are in effect, so customers can choose to delay such electricity-intensive chores as dish washing and clothes drying. Steve Higginbottom, a Gulf Power spokesman, says customers in the program save an average of 15 percent on their electricity bill. Similar time-of-use experiments are under way in New York, California, Washington, and other states to help homeowners get more control over their energy costs. That's the ultimate in thermostat intelligence?knowing when to flip the switch and when to leave it alone. After all, the most cost-efficient appliance is the one that isn't running.

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