Example Data Table
| Appliance |
Typical load |
Suggested design note |
Input use |
| Tankless water heater |
180,000 BTU/hr |
High demand during firing |
Add full nameplate load |
| Gas furnace |
80,000 BTU/hr |
Seasonal steady load |
Add expected simultaneous load |
| Cooking range |
65,000 BTU/hr |
Check all burners and oven |
Use nameplate rating |
| Outdoor grill |
50,000 BTU/hr |
Often on separate branch |
Include branch length |
Formula Used
Adjusted Load: Design Load = Connected Load × Diversity Factor × (1 + Safety Margin ÷ 100)
Gas Flow: Flow in ft³/hr = Adjusted Load ÷ Propane Heat Value
Equivalent Length: Equivalent Length = Straight Length + Fittings Equivalent Length
Velocity: Velocity = Volumetric Flow ÷ Internal Pipe Area
Pressure Drop: Darcy-Weisbach relation is used for friction loss. The calculator estimates Reynolds number and friction factor for each pipe size.
Static Effect: Static loss is estimated from vapor density and vertical rise. Positive rise increases required pressure.
Regulator Utilization: Utilization = Adjusted Load ÷ Derated Regulator Capacity × 100
How To Use This Calculator
Enter the total appliance demand in BTU/hr. Use appliance nameplates when possible.
Add straight pipe length and estimated fitting equivalent length. Include elbows, tees, valves, and connectors.
Select a pipe material. The calculator uses approximate internal diameters for the selected group.
Enter allowed pressure drop and maximum vapor velocity. Smaller pressure drop limits usually require larger pipe.
Add regulator rating, derating, inlet pressure, and outlet pressure. Review utilization before choosing equipment.
Press the calculation button. The result appears above the form and below the header section.
Download the CSV or PDF file when you need a basic project record.
Construction Use
Propane systems need careful planning before any pipe is cut. A regulator must pass the connected load. The line must also carry vapor without excessive pressure loss. This calculator gives a structured first pass for builders, estimators, and designers. It combines appliance demand, gas heat value, pipe length, fittings, elevation, and material inside one worksheet.
What The Tool Checks
The tool converts total demand into cubic feet per hour. It then adds a diversity factor and a safety margin. Each available pipe size is tested with an internal diameter. The program estimates velocity, Reynolds number, friction factor, pressure drop, and capacity. The smallest line that satisfies the allowed drop and velocity limit is shown as the suggested size.
Regulator Planning
A propane regulator should be selected by inlet pressure, outlet setting, total load, temperature range, vent position, and manufacturer data. This page checks the rated capacity against the adjusted load. It also shows the usage percentage. A high percentage means the regulator has little reserve. That condition can cause poor appliance performance when several burners start together.
Line Sizing Notes
Long runs need more attention than short runs. Fittings, valves, risers, and future branches add resistance. The equivalent length field helps include those items. A vertical rise also changes pressure because propane vapor has weight. The effect is usually smaller than friction, but it is useful on taller buildings and roof runs.
Better Input Habits
Enter the largest expected simultaneous load. Use nameplate values when available. Separate outdoor appliances if they have a different branch. Add length for every elbow, tee, valve, connector, and meter set part. Choose a pressure drop that matches the appliance tolerance. Keep records of assumptions, because they make field review faster and clearer. Export the table after each run. Share the summary with the installer. It helps confirm loads, lengths, margins, regulator reserve, notes, and installation risks.
Field Responsibility
The results are for preliminary planning only. Final propane work must follow local code, fuel gas tables, equipment instructions, and licensed review. Real installations can include two stage regulation, underground pipe, corrosion protection, vent limits, seismic valves, pressure tests, and appliance-specific limits. Use the output to compare options, not to replace a qualified installer.
FAQs
1. Is this calculator for final propane design?
No. It supports early planning only. Final work must follow local code, equipment manuals, and licensed review.
2. What is regulator capacity?
It is the maximum listed BTU/hr flow the regulator can deliver under stated inlet, outlet, and pressure conditions.
3. Why add a safety margin?
A margin allows for starting loads, future appliances, fitting uncertainty, temperature effects, and normal estimating variation.
4. What is equivalent length?
Equivalent length adds extra resistance from fittings, valves, tees, connectors, and other parts to the straight pipe run.
5. Why does pipe material matter?
Different materials have different internal diameters and roughness. Both affect velocity, pressure drop, and available capacity.
6. What pressure drop should I use?
Use the drop allowed by your design basis, appliance requirements, and applicable fuel gas sizing method.
7. Can this handle two stage propane systems?
Yes, it can support preliminary checks. Enter the stage details and use pressure values matching that part of the system.
8. Why does vertical rise affect pressure?
Propane vapor has density. Moving it upward requires pressure, so tall risers can add a small static pressure effect.