What is the size of the relief vent on a circuit vented soil branch installation of plumbing fixtures?

In a circuit vented soil branch installation, the size of the relief vent is typically designed to be ½ times the diameter of the soil pipe. This sizing is based on established plumbing codes and standards which dictate proper venting practices to ensure that drains function efficiently while preventing siphonage or negative pressure in the system.

The reasoning for making the relief vent half the size of the soil pipe is to allow for adequate airflow while minimizing the risk of excessive back pressure on the drainage system. This sizing helps maintain a balance between effective drainage and proper ventilation, ensuring that air can move freely in and out of the system to facilitate waste removal without causing blockages or pressure build-up.

The other choices suggest larger diameters relative to the soil pipe, which may not provide the same level of efficiency or could even introduce complications in the venting system. Understanding the correct sizing is vital for maintaining the performance and longevity of plumbing installations.