What does a change cheek elbow allow in terms of duct configuration?

A change cheek elbow is specifically designed to facilitate a size alteration of ductwork without necessitating an elevation change. This is particularly useful in HVAC systems where maintaining a certain height is critical due to space restrictions or design requirements. The cheek provides the necessary geometry to reduce or increase the size of the duct while keeping the airflow path level, thereby ensuring minimal disruption to the air movement and system efficiency.

Other configurations mentioned, like changing airflow direction or connecting two straight ducts, can be managed with different elbow designs or fittings. Similarly, transitioning between different duct types often requires specific fittings designed for that purpose, which may not maintain direct elevation levels. Thus, the primary function of a change cheek elbow lies in its ability to adjust size without requiring elevation changes, making it an essential component in certain duct configurations.