What is the purpose of an exhaust fan in an HVAC system?

The purpose of an exhaust fan in an HVAC system is primarily to remove stale air, odors, and moisture from a building. This function is essential for maintaining indoor air quality and ensuring a comfortable environment. When stale air, which may contain pollutants, excess humidity, or unwanted odors, is expelled from a space, it creates a negative pressure that allows fresh air to enter from outside. This exchange helps to balance air quality and reduces the buildup of contaminants that can affect occupant health and comfort.

In contrast, increasing temperature inside a building or recirculating heated air focuses on maintaining a specific indoor climate rather than removing undesirable elements from the air. Additionally, while distributing fresh air is important for ventilation, it does not encapsulate the primary role of an exhaust fan, which is specifically aimed at expelling air that is no longer fresh. Therefore, the correct answer reflects the exhaust fan's critical role in enhancing overall indoor air quality through the removal of stale air and other unwanted elements.