A gas system serves a longest run of 80 ft to the most remote appliance, which needs 90 cfh. The table for 80 ft gives 3/4 in = 82 cfh and 1 in = 155 cfh. What size serves that final branch?

Explanation

At the 80 ft longest length, 90 cfh exceeds the 82 cfh capacity of 3/4 in pipe, so 1 in (155 cfh) is required. In the longest-length method every section of the system is sized using the single longest run, not each section's own length. This conservative method avoids undersizing under worst-case simultaneous demand.