What is the minimum cross-sectional dimension required for combustion air ducts?

The minimum cross-sectional dimension required for combustion air ducts is indeed 3 inches. This specification is important because properly sized ducts ensure adequate airflow for combustion processes, allowing appliances to operate safely and efficiently. If the ducts are too small, it can lead to insufficient air supply, which may cause incomplete combustion, elevated carbon monoxide levels, and reduced efficiency of heating systems.

In HVAC systems, the sizing of combustion air ducts follows specific codes and standards to maintain safety and performance. A duct with less than 3 inches in width may not provide enough volume for the required airflow, resulting in the issues mentioned above. Ensuring that the duct dimensions meet or exceed this minimum helps in maintaining a safe environment and proper functioning of combustion appliances.