Settings and the time and date are automatically saved, and will remain even after a blackout. This thermostat is compatible with a few more heating and cooling systems than the RTH4300B, accepting systems with heat pumps that don't use auxiliary heat. Only systems with back-up heat, multi-stage heating/cooling systems and electric baseboard heat are incompatible. Programming can be set for weekdays and weekends separately, allowing up to 4 different temperatures to be set throughout the day. This can save up to 33% on the home's heating and cooling costs annually.