This multiple-part article series will discuss the basics, codes and standards, and the science behind chimneys. It will show how back drafting affects chimney performance, while explaining the principles of positive pressure. It will explain how to create and use positive pressure so chimneys will draft for safety and performance.
Many cities have a combustion appliance zone (CAZ) policy to ensure the safe elimination of flue gases from the building. The U.S. Department of Energy (DOE) defines CAZ as any contiguous air volume within a building that contains a combustion appliance. The zone may include, but is not limited to, a mechanical closet, mechanical room, or the main body of a house. Back drafting is the spillage of combustion byproducts into the home, instead of venting out through the chimney or flue.