Which type of draft relies solely on atmospheric pressure?

The correct answer is natural draft. Natural draft is a mechanism that relies entirely on the difference in atmospheric pressure and temperature to create airflow. This type of draft happens due to the natural buoyancy of hot air, which rises and creates a lower pressure area at the base of a chimney or flue. As warmer air rises, cooler air is drawn in from below, promoting the circulation of air necessary for processes such as combustion.

In contrast, induced draft and forced draft involve mechanical systems that actively push or pull air through the system. Induced draft uses fans to draw exhaust gases from the system, while forced draft employs fans to force air into the combustion chamber. Balanced draft combines both induced and forced draft systems to optimize airflow but does not rely solely on atmospheric pressure like natural draft does. Hence, natural draft is distinctly characterized by its reliance on atmospheric conditions rather than mechanical assistance.