To prevent chimney backdrafts, how many inches must the chimney be constructed above the highest point of the roof?

The correct requirement for chimney height above the highest point of the roof to prevent backdrafts is indeed 24 inches. This height is specified in building codes and standards to ensure that the chimney effectively exhausts combustion gases and maintains proper airflow. When a chimney is raised to this minimum height above the roofline, it helps to create a sufficient draft, allowing smoke and gases to escape efficiently rather than being drawn back into the home.

Additionally, constructing the chimney at this height mitigates the risk of downdrafts created by wind interaction with the roof. The height creates a better balance with atmospheric pressure, contributing to stable combustion venting. This is critical for maintaining indoor air quality and safety by ensuring that hazardous gases do not enter living spaces.

In contrast, heights shorter than 24 inches may not create the necessary conditions to establish an effective draft, leading to potential safety hazards associated with backdrafting. Therefore, adhering to this specific height requirement is essential for both safety and operational efficiency of the chimney system.