Chimney Sheep Oblong Chimney Draught Excluder (D)8" (W)20". This Chimney draught excluder is a simple way to block draughts & reduce heat loss through unused open fireplaces. Its clever design works by being a little bit bigger than the flue so it can grip on to the sides & hold itself in place. Simply push up into the narrow part of chimney flue just above fireplace & pull back out before using the fire