What causes a natural draft in a chimney or vent?

A natural draft in a chimney or vent is primarily caused by the height and temperature difference between the inside of the chimney and the outside environment. As the air inside the chimney heats up, it becomes less dense and rises, creating a pressure difference that draws cooler air into the system from below. The height of the chimney enhances this effect, as a taller chimney establishes a stronger draft due to the increased vertical column of warmed air.

This principle is governed by the basic laws of physics, specifically how warmer air rises and creates a lower pressure area at the bottom, pulling in air from the living space or combustion area. The combination of these factors is what effectively facilitates a consistent, natural airflow within the chimney or vent, crucial for the efficient exhausting of gases produced during combustion.

While fan operation can influence airflow, it creates a forced draft rather than a natural one. Gas pressure fluctuations can affect combustion efficiency but are not the primary cause of a natural draft, and adjustable dampers are tools to control airflow rather than initiate a draft naturally.