What type of draft is produced by the difference in weight between flue gases and outside air?

Natural draft occurs due to the buoyancy or difference in weight between the lighter flue gases and the heavier outside air. When the combustion gases are expelled from the system, their lower density compared to the surrounding cooler air creates a vertical movement of air; this is because warm air rises. This phenomenon relies solely on natural convection—no mechanical assistance is needed from fans or blowers.

In the context of propane gas systems, using natural draft can be advantageous in certain settings, as it can simplify the design and reduce the need for electrical components. Systems that utilize natural draft must be carefully designed to ensure the necessary draft pressure is achieved to allow efficient venting of exhaust gases, which is crucial for safety and performance.

In contrast, other draft types, like forced, mechanical, or induced drafts, utilize fans or blowers to assist in moving air or flue gases. These methods are generally employed in systems where enhanced airflow or pressure is required due to specific design or operational constraints.