The U.S. Department of Energy recommends setting the central air thermostat to 78 degrees Fahrenheit during the summer months to conserve energy and reduce energy costs. When a home is unoccupied, raising the thermostat to a temperature of 82 F to 85 F can further reduce energy costs.
The operating cost for central air conditioners increases up to 8 percent for every degree the thermostat is lowered. If 78 F is too warm, especially on the hottest days of summer, set the thermostat as high as possible while maintaining a comfortable temperature. Using a programmable or "smart" thermostat can help take the guesswork out of home cooling needs by raising and lowering temperatures at predetermined times throughout the day.