What component is installed in square throat and heel elbows to allow for better air flow characteristics?

The correct answer focuses on the role of turning vanes in enhancing airflow characteristics within square throat and heel elbows. Turning vanes are specifically designed to streamline the flow of air as it passes through these elbows, which are common in duct systems. When air changes direction abruptly, it can create turbulence, leading to increased resistance and reduced efficiency.

By incorporating turning vanes, the airflow is guided more smoothly around the corners of the elbow. This minimizes turbulence and helps maintain a consistent velocity across the ductwork, improving overall system performance. The use of turning vanes can also lead to reduced noise levels and lower energy consumption, making them a vital component in HVAC systems that involve duct transitions.

Other components listed have different functions; for example, hat sections are often used for structural integrity in duct construction, volume dampers are used to regulate airflow in different parts of the duct system, and backdraft dampers prevent airflow in the opposite direction. None of these serve the specific purpose of improving the flow characteristics within square throat and heel elbows like turning vanes do.