What is the minimum vent size for a 3-inch drain?

The minimum vent size for a 3-inch drain is 1.5 inches, making it the correct choice in this scenario. Vent pipes are essential in plumbing systems as they allow for the release of sewer gases and help maintain proper pressure in the drainage system by preventing vacuum conditions. The International Plumbing Code specifies the minimum vent sizes based on the size of the drain it serves. For a 3-inch drain, a 1.5-inch vent ensures adequate ventilation, which is critical for the proper function of the drainage system, minimizing the risk of blockages and ensuring the safe operation of fixtures connected to the drain.

In contrast, a vent pipe that is too small would not provide effective air flow to equalize the pressure in the drain lines, potentially leading to siphoning and subsequent drainage issues. Likewise, larger vent pipes, such as 2 inches or 3 inches, may exceed the minimum requirements but are not necessary and can result in unnecessary material use and cost without providing additional benefits.