What size of drain is needed for a 3" riser?

The appropriate size of the drain for a 3" riser is 1-1/4 inches or larger. This is based on hydraulic calculations and the need to ensure proper drainage flow from the system. A larger drain helps accommodate the volume of water that may be discharged from a riser of that size, especially considering potential factors like pressure and flow rates during activation of the sprinkler system.

Using a drain size that meets or exceeds this specification minimizes the risk of backflow or blockage, allowing water to flow freely and preventing issues that could arise from insufficient drainage. This sizing is aligned with industry standards and guidelines for fire protection systems, ensuring both effectiveness and safety during operations.