It is incredible how much soot and smoke can get sucked in by a vent in a residential HVAC system during a fire. Depending on the location of the opening in relation to the fire, a return can circulate the smoke throughout the house causing more damage.
For this reason a complete cleaning of the duct system is usually required to keep from recirculating airborne smoke and soot throughout the house. Generally a good indicator for if the system needs to be cleaned is by taking a look at the filter.
For duct cleaning after a fire, or anytime, call SERVPRO of Springfield at 217-528-7775