On this site I found this advice: "If the fireplace is never used, it may be advisable to cover it and seal off completely. It is necessary to fit a 'hit and miss' ventilator to provide ventilation for the flue." Why should the room require ventilation through the flue? No other room has such ventilation. If there is no combustion occurring in the room and the room is heated by the furnace through ductwork (like the rest of the house), why the need for ventilation through the chimney? And what is a "Hit and Miss ventilator"?