Question 18

The MINIMUM required vent size is 4 inches.

Based on the total connected load of 450 drainage fixture units and the length of the stack vent being 25 feet, the minimum required vent size is determined to be 4 inches.

A) 2 1/2 inches

This option is incorrect as a 2 1/2 inch vent size would be inadequate for a connected load of 450 drainage fixture units. Standards typically require larger vent sizes to ensure proper air flow and prevent negative pressure in the drainage system.

B) 3 inches

While a 3 inch vent may be suitable for smaller connected loads, it does not meet the requirements for a load of 450 drainage fixture units. Therefore, this option is also incorrect as it fails to provide sufficient capacity for venting.

C) 4 inches

This is the correct answer because a 4 inch vent is adequately sized for the specified load and length of the vent. It complies with plumbing codes that ensure proper venting and air circulation, reducing the risk of drainage issues.

D) 5 inches

Although a 5 inch vent would be larger than necessary, it is not required given the load and length specified. Therefore, while technically it may handle the load, it does not represent the minimum required size, making this option incorrect.

Conclusion

The minimum required vent size is definitively 4 inches, as it balances the need for adequate air flow with the connected load of 450 drainage fixture units. Options A and B are too small, while D exceeds the minimum requirement without necessity. Thus, option C is the only choice that aligns with standard plumbing regulations for this scenario.