Fireplace dampers are located just above the fireplace opening in the area also known as the throat.  The purpose of the damper is to regulate the amount of air that goes up the chimney during the use of your fireplace.  Also these dampers (when in the closed position) are designed to reduce any of  the heat from within the home going up your chimney when the fireplace is not in use.  We also recommend a set of glass doors for your fireplace to help with keeping the heat in your home and not going up the chimney when the fireplace is not in use.