This illustration explains the physics behind an efficient chimney system and how it improves airflow inside a fireplace. When a fire burns, it produces hot smoke and gases that naturally rise upward because hot air is lighter than cold air. This upward movement creates a pressure difference, known as the stack effect, which pulls fresh air into the fireplace to keep the fire burning. The narrow section called the throat helps control and direct the rising smoke into the main vertical flue. On t