What is the purpose of "Joist Liner"?

The purpose of a joist liner is to effectively convert the floor joist space into a functioning return air duct. This is an important aspect of HVAC design, as it allows air to be effectively returned to the heating or cooling system from various parts of a building using the existing structural framework. Utilizing the joist space as a return air path enhances airflow efficiency and can help to distribute ambient air more evenly throughout a space.

In this context, the return air system is crucial for maintaining balanced air pressure within the building and for ensuring that the HVAC system operates at optimal efficiency. The joist liner specifically provides the necessary surface to direct the airflow correctly, which is key for proper air handling and overall comfort in the environment.

Other options describe functions that pertain to different aspects of HVAC systems. For example, using floor joist space as a supply duct would not effectively function in the same way as a return air system, and the choices regarding insulation directly relate to aspects of thermal management rather than airflow direction. Therefore, the selection of the purpose of a joist liner as making the floor joist space act as a return air duct highlights its specific role in HVAC applications.