Massachusetts Plumbers Journeyman Practice Exam

How should the standpipe for a clothes washer be sized for commercial laundromats?

1. 1 inch in diameter

2. 1½ inches in diameter

3. 2 inches in diameter

4. 2½ inches in diameter

The correct answer is: 2 inches in diameter

The correct answer involves understanding the plumbing requirements specific to commercial laundromats, especially regarding the standpipe size needed for clothes washers. A standpipe serves as the vertical drainage pipe that receives wastewater from the washing machine. In commercial settings, such as laundromats, multiple machines are often operating simultaneously, which leads to a higher volume of wastewater that needs to drain efficiently. The size of the standpipe must accommodate this higher drainage flow: a 2-inch diameter pipe is typically recommended. This size allows for sufficient drainage capacity, reducing the risk of clogs and ensuring that wastewater can be discarded quickly and efficiently, essential for maintaining operations without interruptions. Choosing a smaller diameter, such as 1 inch or 1½ inches, would not provide the necessary capacity for a laundromat's demands, potentially leading to backups and drainage issues. Larger sizes, such as 2½ inches, while they could handle the flow, may not be standard for this application, potentially leading to unnecessary expense and complexity in installation. Hence, the common and effective choice for a commercial laundromat setting is a 2-inch standpipe.