Systems and methods are described for a HVAC control system. An apparatus, includes: a microcontroller; a digital temperature sensor coupled to the microcontroller; a liquid crystal display coupled to the microcontroller; a set of cursor buttons coupled to the microcontroller; a first data structure of personal identification numbers coupled to the microcontroller; a second data structure of historical system usage data coupled to the microprocessor; an upload software thread coupled to the microprocessor and to the first data structure; a billing computer coupled to the second data structure; a real time clock coupled to the microcontroller; and a back up power supply coupled to the real time clock.