What is the minimum vent size allowed for a fixture?

The minimum vent size allowed for a fixture is 1.5 inches. This specification is important in plumbing codes because it ensures adequate airflow to prevent the buildup of negative pressure in the drainage system, which can lead to siphoning of trap seals. A vent that is too small may not effectively allow air to enter the system as water flows, resulting in drainage issues. The 1.5-inch minimum is a standard requirement for many residential plumbing fixtures, striking a balance between effective venting and space considerations within the plumbing infrastructure. This ensures that the plumbing system functions efficiently and remains compliant with established building codes.