What is the proper size for a vent pipe compared to the drain size?

The correct answer regarding the size of a vent pipe compared to the drain size is that the vent pipe should typically be half the size of the drain. This sizing guideline is based on the need for proper venting in plumbing systems to maintain the balance of air pressure within the drainage system. A vent pipe serves to allow air into the drainage system to prevent vacuum conditions that could impede drainage flow.

Having a vent that is appropriately sized (in this case, half the diameter of the drain) ensures that adequate airflow can occur without restricting the drain's ability to transport wastewater effectively. If the vent pipe were the same size as the drain or larger, it could lead to unnecessary complexity in the system and potential plumbing inefficiencies.

This sizing rule helps maintain optimal function while ensuring that the vent works to prevent siphoning and trapping of gases. Ultimately, following this guideline supports proper drainage and venting in compliance with plumbing codes.