What is the minimum size for a wet vent without a toilet?

The minimum size for a wet vent without a toilet is 1 1/2 inches. Wet venting is a plumbing technique that allows the plumbing system to use a single pipe to both vent and carry wastewater. When designing a system that includes sinks, bathtubs, or other fixtures without a toilet, a 1 1/2 inch diameter pipe is typically adequate to handle the flow of wastewater while providing sufficient venting capacity. This size helps prevent potential issues such as siphoning of the traps or poor drainage. It ensures that the fixtures can drain effectively while maintaining an adequate air supply to prevent any negative pressure in the system.

Larger pipe sizes, such as 2 inches or upwards, may not be necessary for these situations, as they can be over-engineered for the requirements of wet venting without a toilet. A 1-inch pipe is generally too small to accommodate the necessary flow rate and venting needs. Thus, a 1 1/2 inch size strikes a balance between functionality and compliance with plumbing codes. This knowledge is critical for ensuring effective drainage and proper plumbing system operation.