The standpipe and trap for an automatic clothes washer should have a minimum diameter of what size?

The minimum diameter of the standpipe and trap for an automatic clothes washer should be 2 inches. This size is specified to ensure adequate drainage and prevent clogs that can occur with smaller diameters. A 2-inch diameter can handle the volume of water that typically discharges from a washing machine, accommodating the rapid influx of water during the machine’s operation while allowing for proper venting to avoid creating a vacuum. This helps to maintain the necessary flow rate and prevents any potential backup or overflow issues that could arise with a smaller pipe. Using the appropriate diameter is crucial for both performance and compliance with plumbing codes that dictate proper installation practices for appliances.