The Department of Energy recommends setting a thermostat at 68 F during winter and 78 F during summer. Setting a thermostat to cooler temperatures in winter slows heat loss, while a warmer setting in summer slows the entering heat.
Ideally, thermostats should be set lower at night or while away from home. Discovery News recommends setting the thermostat at around 62 F at night or while away. While away from home or in the evenings during the summer, thermostats should be set at higher than 78 F to save energy and slow the flow of hot air entering the home.