NFPA 14 Standard for the Installation of Standpipe and Hose Systems Practice Exam

Standpipes and branch lines must be at least 2½ inches in diameter. This minimum size is chosen to ensure adequate flow for firefighting operations while keeping friction losses at a practical level. A pipe smaller than 2 inches would restrict discharge and cause excessive pressure drop, making it harder to deliver the needed water when hoses are attached. While larger sizes (such as 3 or 4 inches) can be used where higher flows are required, the standard sets 2½ inches as the minimum to provide a reliable, widely compatible baseline for most standpipe systems.