What factor is critical for the installation of vent pipes?

The critical factor for the installation of vent pipes is their alignment with fixtures. Proper alignment ensures that the vent piping is correctly positioned to allow for the effective movement of air in and out of the drainage system. This assists in preventing negative air pressure, which can lead to slow drainage or traps being siphoned dry. When vent pipes are aligned with the fixtures they serve, it maintains a proper flow of wastewater and allows for a balanced air pressure, which is essential for the efficient operation of the plumbing system. This integration with the fixtures ensures that gases and odors are adequately vented outside, contributing to the overall health and safety of the plumbing environment.