Where vents, including those for direct-vent appliances, penetrate outside walls of buildings, the annular space around such penetrations shall be ______ ______.

The correct completion of the statement is that the annular space around penetrations for vents, including those for direct-vent appliances, shall be permanently sealed. This requirement is crucial for ensuring the safety and efficiency of the ventilation systems in a building.

When vents penetrate the exterior walls, sealing the annular space prevents the intrusion of outside air and helps to maintain a controlled indoor environment. It also reduces the risk of flue gases leaking into living spaces, which can pose serious health hazards. Proper sealing protects against moisture and pests that can enter through any gaps, and it helps to maintain energy efficiency by minimizing air leaks, ensuring that heating and cooling systems work effectively.

This measures aligns with building codes and safety regulations that emphasize the importance of properly sealing any openings in exterior walls to maintain the integrity of the building envelope.