The brick facing of my fireplace is large (5x10 feet). The fieplace isn't used - the chimney is capped (plate with insulation), fibreglass underneath the damper and styrofoam covering the opening sealed with duct tape. However, cold air still comes into the family room by conduction to the point where cool air can be felt. Besides the discomfort, I believe there's quite a heat loss. Would it pay to insulate the external chimney? (It's a one story chimney and in the garage)? If so, what's the best technique and materials? Thanks.