What is the minimum size vent when frost closer is likely?

The minimum size vent when frost closure is likely is typically required to be 3 inches in diameter. This size is necessary to ensure proper venting under conditions that may lead to frost formation. In colder climates or specific geographic areas where frost is a concern, a larger vent diameter helps prevent potential blockages caused by ice or snow accumulation.

Using a 3-inch vent allows for adequate airflow, reducing the likelihood of pressure buildup within the plumbing system and ensuring that sewer gases can safely escape. A vent that's too small may not perform effectively in these conditions, leading to a failure in the plumbing system's venting ability. This is why choosing the right size for frost-prone areas is critical for maintaining the reliability and safety of plumbing installations.