For a 1 1/2 inch pipe, the maximum distance from fixture trap to vent is?

• A. 2 Feet 6 Inches
• B. 4 Feet
• C. 5 Feet
• D. 3 Feet 6 Inches

Answer: (D)

Traps must be vented within a limited horizontal distance from the trap to prevent siphoning when the fixture drains. That limit depends on the pipe size. For a 1 1/2 inch drain, the trap arm can extend up to 3 feet 6 inches before a vent is required. This distance balances the need to vent the trap with the practical routing of the piping. So, 3 feet 6 inches is the maximum allowable distance from the fixture trap to the vent for a 1 1/2 inch pipe. The other options are either shorter than the maximum or exceed the allowable limit for this pipe size.