Fuel-Gas Pipe Capacity (Spitzglass)
The inverse of the Spitzglass pressure-drop tile: the max flow a bore carries within an allowable drop - Q = 3550 sqrt(dH D^5 / (SG L K')), K' = 1 + 3.6/D + 0.03 D. A 1 in bore (ID 1.049), 100 ft, 0.6 SG natural gas at a 0.5 in w.c. allowable drop carries 173 CFH at 480 fpm. A longhand alternative to the NFPA 54 / IFGC capacity tables; the actual bore, not nominal, and NFPA 54 governs. Flags a drop above the ~1.5 psi low-pressure range.
Formula and source
Spitzglass low-pressure solved for the flow: Q = 3550 * sqrt((dH * D^5) / (SG * L * K')), K' = 1 + 3.6/D + 0.03*D. dH (in w.c.), D (in actual bore), L (ft), SG. Velocity from Q and bore area.
Published Spitzglass low-pressure gas-flow equation (public engineering formula); the inverse of the gas-pipe pressure-drop tile and a longhand alternative to the NFPA 54 / IFGC capacity tables, by name.
Audience
This tile is built for plumbers and the adjacent professions in the Plumbing and Gas group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.