C-Bus™ Programmable 4 Zone Thermostats are used to regulate the air temperature of up to four separate zones (plus an unswitched zone) by controlling heating/ventilation/air conditioning (HVAC) equipment. The unit can schedule up to four set points during a day, and unique schedules can be programmed for each day of the week. The unit monitors the air temperature using its internal temperature sensor or optionally via an external C-Bus temperature sensor.