How does a natural draft ventilation system operate?

A natural draft ventilation system operates by relying on natural convection rather than mechanical means. Natural convection is the process where warmer air, which is less dense, rises while cooler air remains lower in temperature, creating a difference in density that facilitates airflow.

In this system, as air is heated—whether by a heating unit or other sources—it naturally ascends, and as a result, a vacuum is created at the lower levels that draws cooler outside air into the space. This cycle continues as long as there is a temperature difference; therefore, the movement of air is not dependent on fans or mechanical devices. This makes such systems often simpler and more energy-efficient since they do not require electrical power for operation.

While other options involve mechanical systems or methods of achieving airflow through mechanical means, they do not accurately depict how natural draft ventilation fundamentally relies on the principles of convection and pressure differences caused by temperature variations.