What is the term for a rectangular duct elbow that changes dimensions across the cheek but not across the heel and throat?

The term "Change Cheek Elbow" accurately describes a rectangular duct elbow that alters dimensions across the cheek while maintaining constant dimensions across the heel and throat. This design is specifically used in ductwork to efficiently change the direction of airflow while managing the transition in duct size on just one side, which can be crucial in adjusting airflow dynamics in a ventilation system.

In contrast, a "Transition Elbow" typically refers to an elbow that transitions between different sizes or shapes of ducts, affecting both its cheeks and throat rather than just the cheek area. A "Round Elbow" and a "Square Elbow" refer to elbows that are cylindrical or rectangular, respectively, and these terms do not accurately illustrate the specific characteristic of changing dimensions just at the cheeks. Thus, "Change Cheek Elbow" is the most precise terminology for this specific configuration of ductwork.