Blower Motor and Fan Moves the Heat (Air Handler)
Schedule a professional tune-up every fall (before you first turn on your heating system). They will be able to test your heat exchanger for cracks, clean your pilot light, inspect the ventilation system, and much more.
As the heat circulates through the heat exchanger, the blower motor and fan moves the heat through plenum, and from there through the rest of the ductwork in your home. The heat flows through the various vents in your home to provide you with heat. Once enough heat is generated, the thermostat will shut off the heater.
When there is a problem with your furnace, it is usually the thermostat (control system), gas valve/thermocouple/heat exchanger (heat source), or the blower/air handler/ductwork (distribution system). In any case, a trained and qualified HVAC technician will be able to fix the problem quickly and effectively.