Chimney fans are devices installed at the top of the chimney ducts to improve draft and ensure proper ventilation. They help expel smoke, gases, and fumes efficiently, preventing backdrafts and enhancing combustion in fireplaces, stoves, or boilers. Chimney fans are especially useful in buildings where natural draft is weak due to chimney height, weather conditions, or structural design. They come in different types, including electrically powered and wind-driven models, and can be controlled manually or automatically for optimal performance.