What is considered "return air"?

The term "return air" refers to air that is taken from an approved conditioned space and redirected back to the heating, ventilation, and air conditioning (HVAC) system for reconditioning. This process is essential for maintaining indoor air quality and comfort, as the HVAC system processes this air to redistribute it within the space.

Option C emphasizes that return air is specifically that which has already been conditioned (heated or cooled) and is being cycled back into the system for further processing, making it central to the function of indoor climate control.

The other options describe different scenarios that do not align with the definition of return air. Fresh air introduced from outside is typically referred to as "supply air" rather than return air, as it has not yet circulated through the conditioning process. Conditioned air that is exhausted is typically vented to the outside and does not come back into the system. Air in a static state within ducts does not refer to an active circulation process and is not specifically recognized as return air within the functional context of HVAC systems.