The minimum size pipe permitted for a steel sprinkler system is 1-inch pipe for a new NFPA 13 sprinkler systems according to 2016 NFPA 13: 18.104.22.168 under Plans and Calculations; Hydraulic Calculations Procedures; General
- Pipe sizes shall be no less than 1 inch nominal for black or galvanized steel piping
- No less than 3/4 inch nominal for copper tubing or brass, stainless steel or nonmetallic piping listed for fire sprinkler service
However, the standard seems to indicate in several instances that asslong as the pipe size selected is determined through hydraulic calculation, any pipe sizes can be selected.
" The minimum size of the riser shall be 4 in. (100 mm)
unless hydraulic calculations indicate that a smaller size
riser will satisfy sprinkler and hose stream allowances."
"The pipe sizing schedules provided shall not apply to hudrauhydraul calculated systems."
Please kindly advise of the min. 1" size requirement is applicable for all cases, including when hydraulic calculation is used.