Use the lowest setting you feel comfortable at.
Older thermostats are often inaccurate.
Place a thermometer next to your thermostat to help you set it correctly. If you start to feel chilly, put on another layer of clothes before turning up the thermostat. At bedtime, or when you're away from home, set your thermostat to 55 or less. Turn the temperature down when you leave the house for longer than one hour. Replace standard thermostats with heat-anticipating or electronic thermostats.