A register has been improperly installed in the cold air return ducting. Air which is drawn into this register by the blower will lower the air pressure around the furnace and may cause flue gases, which rise by gravity, to spill from the vent. These flue gases can then be easily drawn into the furnace and distributed through the living area, creating a hazardous condition. The furnace filter is also loose and should be properly secured. (The cover for the blower compartment has been removed for inspection.)