What is the usual duct depth for rectangular sheet metal ducts?

The usual duct depth for rectangular sheet metal ducts is typically 8 inches. This dimension is commonly used in HVAC systems as it provides a balance between space considerations, airflow efficiency, and manufacturing convenience. An 8-inch depth allows for adequate airflow while fitting well within the constraints of standard building designs.

While other depths like 6, 10, or 12 inches might be utilized depending on specific design requirements or airflow needs, 8 inches has become a standard in many installations. This standardization also helps ensure compatibility with various fittings and components in ventilation systems, making it a practical choice for ductwork. Thus, understanding this common dimension is crucial for HVAC professionals when designing and installing air distribution systems.