Which duct fitting changes size from one end to the other without altering the direction of airflow?

The fitting that changes size from one end to the other without altering the direction of airflow is known as a transition fitting. This type of fitting is specifically designed to connect ductwork of different diameters, allowing for a smooth and efficient airflow between two sections. The primary purpose of a transition fitting is to facilitate a change in duct size while maintaining a straight path for the air to flow through.

In HVAC systems, maintaining proper airflow is crucial for efficiency and performance, and using transition fittings helps to minimize turbulence and potential energy losses that could occur with inappropriate duct size changes. This makes transitions vital components in both residential and commercial systems, ensuring they operate effectively despite variations in duct sizes that may arise in different areas of a building.