Low-Pressure Fuel-Gas Pressure Drop (Spitzglass)

Pressure drop (in. w.c.) and velocity for low-pressure fuel gas via the Spitzglass equation.

Run the calculator

Example

You enter

Gas flow (CFH) 1000
Pipe inside diameter (in, actual bore) 1.049
Pipe length (ft) 100
Gas specific gravity 0.6

You get

Pressure drop 16.73
Velocity 2777 fpm

Details, formula, and sources

With a flag when the drop exceeds the low-pressure validity range.

Spitzglass low-pressure: Q = 3550 * K * sqrt((dH * D^5) / (SG * L)), K = 1/sqrt(1 + 3.6/D + 0.03*D). Solved for dH given Q (CFH), D (in actual bore), L (ft), SG. Velocity from Q and bore area.

Published Spitzglass low-pressure gas-flow equation (public engineering formula); the longhand alternative to the NFPA 54 / IFGC capacity tables, by name.

NFPA 54 free read-only at nfpa.org/freeaccess and codes.iccsafe.org; NFPA 54 governs the installation.

Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

Field names used by the API: flow_cfh, id_in, length_ft, sg, drop_inwc, velocity_fpm

Inside diameter actual bore, not nominal pipe sizeSpitzglass equation