What is the minimum vertical drop required from the outlet of a condensate drain pan to the inlet of the P-trap?

The minimum vertical drop required from the outlet of a condensate drain pan to the inlet of the P-trap is commonly established to ensure proper drainage and prevent issues such as backflow or water stagnation. A drop of at least 3 inches is specified because this height helps maintain a continuous flow of condensate, allowing gravity to assist in the drainage process effectively.

This minimum distance is important for establishing a proper functioning drainage system, as insufficient drop could lead to the possibility of debris or air locks which can impede the flow, potentially causing leaks or overflow. Additionally, adhering to this requirement helps comply with building codes and best practices for plumbing systems related to HVAC applications.

The other options, while they may seem reasonable, do not meet the established guidelines or industry standards for ensuring that the drainage system functions effectively and reliably. Thus, 3 inches is the correct minimum drop required in this context.