The picture above was taken on a job I did this weekend in Newtown Square. This is a picture looking up the chimney in from the fireplace. This is the area called the smoke chamber and is generally the “weak link” of any fireplace system. Many times these areas are not built thick enough, lack the proper clearance to combustibles, and are not built smooth. The function of the smoke chamber is to contain the heat, smoke, and other products of combustion. When the smoke chamber is not parged smooth with cement, it leaves a rough path for the smoke to follow which will hinder the flow of smoke up the flue. The smoke chamber in the picture above is missing many of the mortar joints between the bricks and there are various gaps throughout the entire chamber. Any gap or missing mortar joint is a potential area where heat can transfer through and ignite nearby combustibles. The picture below is the same smoke chamber after I repaired it by parging the entire thing with a high temperature cement. Not only will this help keep the heat from transferring through the bricks, missing joints, or gaps, it will also improve the flow of smoke up the chimney by giving it a completely smooth path to follow.