What is the minimum size for a tub and overflow vent?

The minimum size for a tub and overflow vent is 1-1/2 inches. This size is commonly specified in plumbing codes and regulations to ensure that the venting system adequately allows for the proper drainage of the tub while preventing trap siphonage. A 1-1/2 inch vent provides sufficient airflow to equalize pressure within the drainage system, which is essential for maintaining a functional plumbing setup.

Choosing a size lower than 1-1/2 inches may not provide adequate venting capacity, potentially leading to drainage issues such as slow draining and gurgling sounds. Although other sizes could theoretically be used in different contexts, the specific requirement for the tub and overflow vent ensures effective performance and compliance with plumbing standards.