Work back from the load to the main: total load, building piping, meter, service regulator, service line and excess flow valve. Natural gas or propane vapor, sized for industrial and commercial services as well as small services.
| Equipment | Input | Units | Qty | Diversity | SCFH |
|---|
| Size (in) | Actual ID (in) | Capacity (SCFH) | Capacity (MBH) | % used | Status |
|---|
Longest-length method (IFGC 402.4.1): size every section from the meter using the total length to the most remote outlet and the load that section carries. Capacities are computed from IFGC 402.4 Equation 4-1 (under 1.5 psi) or 4-2 (1.5 psi and over) with actual inside diameters; they agree with the published Table 402.4(2) values to within about 1% (Sch 40 1/2 in, 10 ft, 0.5 in. w.c. = 172 CFH).
CSST is sized from tables, not an equation: IFGC Tables 402.4(15)-(19) for natural gas and 402.4(32)-(34) for propane, plus the Gastite, Pro-Flex and HOME-FLEX manufacturer tables. Each nominal size uses its smallest EHD, the next longer tabulated length (no interpolation) and the table at or below your delivery pressure and drop. Capacities are conservative across brands (the lowest value in any source table); confirm with the installed brand's table. TracPipe and WardFlex EHDs fall inside the ranges shown.
| Meter | Rating SCFH | MAOP psig | Capacity at pressure SCFH | % used | Status |
|---|
American diaphragm capacity at pressure is taken from the published "Diaphragm Meter Capacities" table in the Elster American technical bulletin (0.60 SG natural gas, 0.25 to 100 psig): interpolated between published pressures, never extrapolated, and capped at the highest published pressure (flagged) or blocked above MAOP. A model without a published table would use rating × absolute-pressure ratio, labelled "conservative estimate". Rotary capacity = rating × (metering pressure + atmospheric) ÷ base pressure, which matches the Dresser ROOTS Series B3 corrected-capacity table; rotary ratings and MAOP are from that brochure. Rotary meters measure actual volume regardless of gas; diaphragm ratings for propane should be confirmed with Caddy Controls. Refurbished American meters and ROOTS meters are available through Caddy Controls.
| Family | Max inlet psig | Outlet range psig | Family max SCFH | % of max | Status |
|---|
Family limits are from the Dresser ROOTS Regulator Product Line Catalog (DUS.ROOTS.009a). "Family max" is the largest flow the family can deliver with its biggest orifice and best inlet pressure, not the capacity at your inlet pressure: confirm orifice and spring from the model's capacity tables. Dresser notes spring-loaded service regulators are not to be used above 60 psig inlet without additional overpressure protection. Overpressure protection (relief or monitor) is required by 49 CFR 192.195/192.197; size it separately.
| Pipe | ID (in) | Pressure at regulator (psig) | Drop (psi) | Velocity (ft/s) | Max length (ft) | Status |
|---|
49 CFR 192.383: EFVs are required on new or replaced services to single-family residences, multifamily services and single small commercial customers with a known load not exceeding 1,000 SCFH based on installed meter capacity, unless an exception applies (for example the line does not operate at 10 psig or more all year). 49 CFR 192.385: services with installed meter capacity over 1,000 SCFH need a manual service-line shut-off (curb) valve or, where engineering analysis supports it, an EFV. Trip is checked at the minimum main pressure, where it is lowest. The EFV drop entered here is subtracted from the main pressure in the service-line calculation.
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