An energy saving controller for an air handler having a fan and a heater or a compressor, the energy saving controller having circuitry for monitoring of ON and OFF durations of the heater if the air handler is in a heating mode, or the compressor if the air handler is in a cooling mode, in a previous cycle, and, of ON duration of a current cycle, and determining the fan's first run time extension based on the ON and OFF durations of the previous cycle and the ON duration of the current cycle.