What is the main drain size required for risers measuring 2½ inches to 3½ inches?

The main drain size required for risers measuring 2½ inches to 3½ inches is specified to be 1¼ inches. This size is essential for ensuring adequate drainage and to maintain the proper function of the fire sprinkler system. A 1¼ inch drain allows for efficient water flow and ensures that any residual water can effectively be drained from the risers after testing or discharging, thus minimizing the risk of water logging and promoting quick, efficient maintenance.

Selecting the correct drain size is crucial for compliance with relevant standards and codes which ensure the system operates effectively under varying conditions. A drain that is too small may lead to slow drainage and potential problems like backup or incomplete draining, while a larger size is often unnecessary and could complicate installation and maintenance without providing additional benefit. Therefore, using a 1¼ inch drain for this range of riser sizes is the established best practice in the industry, aligning with specified codes for sprinkler systems.