What does the exhaust air duct primarily do?

The primary function of an exhaust air duct is to remove air from spaces such as kitchens and bathrooms. These areas often generate moisture, odors, and pollutants that need to be vented out to maintain indoor air quality and prevent issues like mold growth. By directing stale or contaminated air outside, exhaust air ducts help ensure a healthier environment.

In contrast, the other options relate to different aspects of air management in HVAC systems. Providing heating pertains to systems that distribute warm air, while supplying conditioned air refers to delivering cooled or heated air into living spaces. Recirculating air involves reusing indoor air since it reduces energy use but doesn’t specifically address ventilation needs in areas with high humidity or strong odors like cooking or bathing. Hence, the role of the exhaust air duct is distinctly focused on ventilating spaces to effectively manage air quality.