A combination waste and vent pipe connecting to the building drain with a total of 29 DFU shall be what size?

In plumbing design, the sizing of combination waste and vent pipes is critical for proper drainage and venting of fixtures in a residential setting. The size of these pipes is determined based on the Drainage Fixture Units (DFU) that the system will serve.

For a total of 29 DFU, the correct size of the combination waste and vent pipe is established by local plumbing codes and tables that specify the required pipe diameter based on the number of fixture units. Typically, for a combination waste and vent system with a load of 29 DFU, the pipe must be at least 4 inches in diameter. This size ensures that the system can effectively transport waste without becoming clogged and can also allow for adequate venting to prevent siphoning effects that could compromise drainage.

Moreover, a 4-inch pipe provides sufficient capacity to handle the flow and waste from the fixtures, reducing the risk of blockages and ensuring optimal performance of the plumbing system. If a smaller pipe size were used, it could lead to inadequate drainage and potential sanitary issues, making the 4-inch size the appropriate and safest choice for this specific DFU load.