521 (Tekmar) | Programmable Tstat 2 Ht/ Ht-CoolThe Programmable Thermostat 521 is Designed For Three Different Modes of Operation: Single Stage Heating, Two Stages of Heating With a Fan, or One Stage of Heating And One Stage of Cooling With a Fan. Two Auxiliary Sensors May be Added to Measure The Floor, Outdoor or Room Temperature. A Slab Sensor 079 is Included to Measure Floor Temperature to Protect The Floor From Overheating And Enhance Comfort. The Programmable Schedule Supports Either a 7 Day