What type of ducts are installed below ground level?

The correct answer identifies underground ducts as the specific type of ducts designed for installation below ground level. Underground ducts are typically utilized for various purposes, such as conveying air for heating, ventilation, and air conditioning systems. Their design often takes into account factors such as soil pressure, moisture, and temperature variations, ensuring they can manage the environmental conditions found beneath the surface.

Understanding this distinction is essential for both the installation process and maintenance of HVAC systems, as underground ducts may require particular materials and insulation to prevent issues such as condensation or sagging. While other duct types exist, they either function in aboveground applications or are classified based on their role in the HVAC system, rather than their installation location.