A chimney back refers to the back wall or lining of the chimney in a fireplace or furnace. In an older chimney, this back is often made of fire-brick masonry or ornamental metal. The design of such a chimney wall is formed to reflect heat back into the room. It helps to protect the house from ember fires while enhancing heat production of the fireplace. It is important to have the chimney back inspected prior to purchasing a home. Cracks in the back or the lining of the fireplace can lead to fires or carbon dioxide build-up. A good chimney mason can replace this chimney component with new fire-brick or with a modern synthetic liner. However, this job can be expensive and should be part of the sale price negotiations if it needs replaced or repaired.