In a commercial ejector vent system, within how many feet of a 3 inch vent stack can the vent be reduced to 2 inches?

• A. 15 feet
• B. 25 feet
• C. 50 feet
• D. 100 feet

Answer: (B)

In a commercial ejector vent system, vent sizing is about ensuring enough air can enter the system to prevent trap siphonage. A larger vent near the vent stack provides the needed capacity for the ejector pit and nearby fixtures. Reducing the vent size too soon would limit that air access and risk siphoning or gurgling in nearby traps. Codes allow reducing a 3-inch vent to 2 inches only after a certain distance from the vent stack to keep enough venting capacity downstream. That distance is twenty-five feet. So, you can downsize from 3 inches to 2 inches no closer than 25 feet from the vent stack. Reducing earlier would compromise venting; delaying the reduction beyond 25 feet would exceed the allowed limit and isn’t permitted.