Gas Pipe Sizing Calculator - IFGC/IRC Pipe Diameter by BTU Load

How It Works

1. Select Fuel Screen and Pressure Drop

   Enter specific gravity for the fuel-gas screen and choose a pressure-drop allowance. The app uses local heating-value and pressure-factor fixtures, so final sizing still needs the adopted fuel-gas code, utility, manufacturer, and AHJ basis.

2. Add Appliance Input Ratings

   Enter appliance nameplate input BTU/hr ratings. The built-in appliance buttons are local placeholders only; output ratings and efficiency-adjusted heat output are not the correct input for pipe capacity.

3. Enter Equivalent Run Length

   Use total equivalent length, not just straight-run tape measurement. Include fittings, valves, tees, meters, regulators, flexible connectors, elevation effects, and manufacturer equivalent-length requirements.

4. Choose Local Pipe Row Set

   Choose black iron, CSST, or copper Type K local row sets. CSST and copper acceptance are especially manufacturer- and jurisdiction-specific, so the app rows are not approval tables.

5. Review the Local Capacity Calculator

   The output shows the first local row whose calculated capacity is above the entered demand. Verify final pipe size, material, regulators, combustion air, venting, testing, purging, permits, inspections, and utility acceptance outside the app.

Built For

• Plumbers doing a first-pass BTU and equivalent-length check before code-table verification
• HVAC contractors screening whether a furnace, water heater, or generator addition needs deeper gas-piping review
• Mechanical designers comparing local pipe-row sensitivity before using adopted IFGC, IRC, NFPA 54, or manufacturer tables
• Home inspectors documenting that existing fuel-gas piping needs qualified follow-up before added load is approved
• LP gas dealers screening propane pipe capacity before checking tank, regulator, vaporization, supplier, and NFPA 58 requirements
• Permit reviewers and owners using the result as a question list, not as approval documentation

Features & Capabilities

Equivalent-Length Input

Accepts one equivalent run length for the screened path. The app does not build a branch network or replace the code longest-run table workflow.

Spitzglass-Style Calculator

Calculates capacity from local internal-diameter rows, specific gravity, equivalent length, and a pressure-drop factor. This is a planning formula calculator, not a protected code-table reproduction.

Local Row Sets

Includes local black iron, CSST EHD, and copper Type K row sets. Manufacturer, listing, gas composition, and jurisdiction rules control final material acceptance.

Natural Gas and LP Screening

Uses local heating-value fixtures for natural-gas and LP-gas style screens. LP systems still need tank, regulator, vaporization, storage, supplier, NFPA 58, and AHJ review.

Capacity and Velocity Output

Shows local capacity, demand, velocity, and capacity margin for each bundled pipe row so users can see where the local screen becomes tight.

Source Warning Export

Report and PDF exports carry the same source and safety boundary warnings as the visible app so the result is not separated from its limitations.

Assumptions

• Capacity is calculated with a local Spitzglass-style formula and local internal-diameter rows, not a direct protected code table.
• Heating value is a local fixture: 1030 BTU/CFH for SG below 1.0 and 2516 BTU/CFH for SG 1.0 or higher.
• Pipe row sets are local black iron, CSST EHD, and copper Type K fixtures that require row-by-row validation before use.
• All entered appliances are treated as connected input load; diversity, simultaneity, branch layout, regulator layout, and table rounding are not fully modeled.
• Equivalent run length must be supplied by the user and should include fittings, valves, meters, regulators, connectors, and elevation effects.
• Pressure-drop selection is a screening input only and does not prove appliance inlet pressure, regulator, meter, utility, or AHJ acceptance.

Limitations

• Does not reproduce or validate current IFGC, IRC, NFPA 54, or NFPA 58 sizing tables.
• Does not build a branch network, segment schedule, regulator layout, meter check, or utility service-capacity check.
• Does not calculate fitting equivalent lengths, elevation effects, connector losses, appliance-train drops, or manufacturer-specific CSST rows.
• Does not determine whether copper, CSST, PE, or any material is allowed in a specific jurisdiction or gas composition.
• Does not size LP tanks, regulators, vaporization capacity, storage separation, or supplier delivery equipment.
• Does not address venting, combustion air, appliance clearances, pressure/leak testing, purging, startup, or inspection acceptance.

References

• NFPA 54 / ANSI Z223.1-2024 - National Fuel Gas Code source pointer
• 2024 International Fuel Gas Code and Appendix A source pointers
• 2024 International Residential Code Chapter 24 Fuel Gas source pointer
• NFPA 58-2024 Liquefied Petroleum Gas Code source pointer for LP-gas context
• Manufacturer instructions, gas utility requirements, adopted local code, and AHJ review for final sizing

Frequently Asked Questions