Low-pressure gas pipe sizing using the Spitzglass formula. Schedule 40 black iron pipe for natural gas and propane distribution.
| Pipe Size | ID (in) | Capacity (CFH) | Velocity (FPS) | ΔP (in.wc) | Status |
|---|
| Application | Max Velocity | Notes |
|---|---|---|
| Low-pressure gas mains | 30 FPS | NFPA 54 / IFGC recommendation |
| High-pressure gas | 50 FPS | Above 0.5 psig |
| Outdoor underground | — | Pressure drop governs; per utility requirements |
| Typical design target | 20–25 FPS | Leaves headroom for demand diversity |
This natural gas pipe quick estimator sizes low-pressure gas runs in Schedule 40 black iron pipe. Enter the gas load in MBH, the gas type (natural gas, propane, or a custom specific gravity), the developed length, and the allowable pressure drop; the tool recommends a pipe size and reports the gas demand in CFH, the gas velocity, and the actual pressure drop, plus a full capacity table for every size.
It is meant for a fast first pass on a single run. Final design should follow the longest-length or branch-length tables in NFPA 54 / IFGC, confirm utility pressure, and account for fittings and local code amendments.
This is the Spitzglass low-pressure form, with Q in CFH, ΔP in inches of water column, D the inside diameter (in), L the developed length (ft), and Sg the specific gravity (≈0.60 natural gas, 1.52 propane). It is the engineering basis behind the low-pressure capacity tables in NFPA 54 (National Fuel Gas Code) and the IFGC. Velocity is checked against the IFGC / NFPA 54 limit of about 30 fps for low-pressure mains, with 20–25 fps a common design target.
This calculator handles one step. AIM Works runs the complete MEP design workflow — thermal load calculations, duct & pipe networks, equipment selection, code compliance, and an AI design assistant — in one tool.
Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.