Why does the fan run on at the end of the heating period for my LSTE?

At the end of the heating period, the fan will run at full speed for 60 seconds before dropping to 20% lower for an additional 60 seconds to flush out any stored heat in the heater. Once this cycle has taken place, the fan will stop running and will not start again until the next heating period. 

Applicable Models:

LST050E, LST075E, LST100E, LST150E