What is the maximum drainage fixture units for a horizontal branch using a 2-inch pipe?

What is the maximum drainage fixture units for a horizontal branch using a 2-inch pipe?

• A. 1 DFU
• B. 3 DFU
• C. 20 DFU
• D. 6 DFU

Answer: (D)

The concept here is drainage fixture units (DFU) and the capacity of a branch line. DFU is a way to compare how much drainage a fixture will add to the piping system. When you run fixtures onto a horizontal branch, you sum their DFUs and compare that total to the capacity allowed by the pipe size on that branch. For a 2-inch horizontal branch, the code specifies a maximum of 6 DFU. That means you can connect fixtures whose total DFU do not exceed 6 on that single 2-inch branch. If you exceeded it, drainage could be slow, siphon traps, or cause venting issues. So the correct maximum is 6 DFU. The other numbers either stay below the limit or exceed what a 2-inch branch can handle on a single horizontal run (for example, 20 DFU would be too high).

The concept here is drainage fixture units (DFU) and the capacity of a branch line. DFU is a way to compare how much drainage a fixture will add to the piping system. When you run fixtures onto a horizontal branch, you sum their DFUs and compare that total to the capacity allowed by the pipe size on that branch. For a 2-inch horizontal branch, the code specifies a maximum of 6 DFU. That means you can connect fixtures whose total DFU do not exceed 6 on that single 2-inch branch. If you exceeded it, drainage could be slow, siphon traps, or cause venting issues. So the correct maximum is 6 DFU. The other numbers either stay below the limit or exceed what a 2-inch branch can handle on a single horizontal run (for example, 20 DFU would be too high).