What is the minimum distance that ducts must be installed above the earth?

The correct choice states that ducts must be installed a minimum of 4 inches above the earth. This requirement is important for several reasons.

Firstly, the elevated positioning of ducts helps prevent moisture from entering the duct system, which can lead to mold growth and degradation of insulation materials. Moisture can accumulate in underground or ground-level ducts, causing significant maintenance issues and compromising indoor air quality.

Secondly, elevating ducts above the earth also protects them from physical damage. Ground-level ducts are more susceptible to impact from vehicles, landscaping equipment, and natural ground movements, resulting in potential leaks or system failures.

Furthermore, maintaining a consistent height for ducts facilitates better airflow and thermal efficiency. It ensures that ducts operate optimally, providing efficient heating or cooling throughout the building.

These safety and performance considerations underline the importance of adhering to the specified minimum height of 4 inches above the surface.