Which of the following is essential for proper duct installation underground?

For proper duct installation underground, sloping for drainage is essential because it prevents the accumulation of moisture within the ductwork. When ducts are installed below ground, they are susceptible to water infiltration or condensation. If the ducts are not sloped correctly, water can collect in low points, leading to issues such as increased pressure drop, reduced airflow efficiency, and potential damage to the ductwork material.

Proper drainage helps maintain the integrity of the HVAC system, ensuring it operates efficiently and prolonging the lifespan of the ducts. Airflow and thermal efficiency can significantly decrease if moisture is trapped, leading to an unhealthy environment and potential for mold growth. Therefore, implementing a proper drainage slope is a crucial aspect of underground duct installation.