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Low Pressure Gas Installations
Gas steel pipe selection
Flow m3/h
Or
Power kW
Local losses (optional)
Low-pressure gas installation pressure drop calculator
Professional calculator for pipe sizing and pressure drop calculations in internal low-pressure gas installations (up to 10 kPa). Calculations are based on the flow velocity criterion (v ≤ 6 m/s) — in accordance with Polish technical regulations and standards PN-M-34501 and PN-EN 1775.
Tool designed for gas installation designers, certified gas installers, and building inspectors. The calculator supports two pipe series — steel (per PN-EN 10255) and copper (per PN-EN 1057) — and for each specified flow rate or gas appliance power output it selects appropriate diameters, determines the unit pressure drop, and calculates the total pressure drop including local resistance losses using the equivalent length method.
How to use the calculator in 3 steps
Enter the gas flow rate in m³/h or the gas appliance power in kW. Values are converted automatically — the calculator assumes typical gas boiler efficiency (approx. 90–97%). For appliances with non-standard efficiency (e.g., instantaneous water heaters), it is recommended to enter the flow rate directly.
Optionally expand the local losses section: enter the pipe section length in metres and the number of fittings (elbows, tees, valves, reducers). The calculator will determine the equivalent length of fittings based on the equivalent length table for the given diameter, then add it to the actual length.
Read the results: for each suitable pipe diameter, the calculator shows the unit pressure drop [Pa/m]. If length and fittings are provided — the equivalent length, total calculated length, and total pressure drop [Pa] are also displayed. Verify that the cumulative pressure drop along the route does not exceed the allowable value (standard limit: 0.5 kPa for internal installations).
What the gas installation calculator computes
Based on the given gas flow rate, the program determines a complete set of data needed to design a gas installation section:
- Recommended pipe diameters — selected so that the gas flow velocity does not exceed 6 m/s (velocity criterion per PN-M-34501).
- Unit pressure drop R [Pa/m] — pressure loss per running metre of pipe for the given diameter and flow rate.
- Equivalent length of fittings [m] — the sum of equivalent straight pipe lengths corresponding to local resistances (elbows, tees, valves) from the table for the given diameter.
- Total pressure drop [Pa] — the product of the unit drop and the calculated length (actual + equivalent). The sum of drops across all sections should not exceed 0.5 kPa.
Input data — what to enter and where to find it
Flow rate [m³/h] or power [kW]
Natural gas (group E) flow rate in m³/h (at normal conditions) or the rated power of the gas appliance in kW. The calculator automatically converts between values, assuming boiler efficiency. Typical values: 24 kW combi boiler ≈ 2.5 m³/h, 4-burner cooktop ≈ 1.2 m³/h, 19 kW instantaneous water heater ≈ 2.0 m³/h. For multiple appliances on one section, sum the flow rates with the simultaneity factor applied.
Section length [m]
Actual length of the gas pipe section in metres — measured along the pipe axis from the starting point (e.g., main valve, tee) to the end point (e.g., gas appliance, next tee). Required for calculating the total pressure drop on the section.
Fittings and valves
Number of individual fittings on the section: elbows (90°), tees (straight-through and branch), ball valves, angle valves, reducers. Separate equivalent length tables are used for steel and copper pipes — the calculator automatically selects the appropriate table. Equivalent lengths depend on pipe diameter: e.g., a DN 25 steel elbow ≈ 1.0 m, while a Cu 22×1 elbow ≈ 0.6 m.
Key considerations when designing a gas installation
The allowable pressure drop in an internal low-pressure gas installation is 0.5 kPa (500 Pa) from the main valve to the most remote appliance — this is a normative value from PN-M-34501. Vertical pipe sections cause pressure changes: pressure increases by approx. 5.4 Pa/m when the pipe runs upward (natural gas is lighter than air). When selecting diameters, consider future installation expansion — adding another appliance will increase the flow rate on the shared section. Steel pipes are joined by welding or threading (up to DN 50), copper pipes — by brazing. Every joint must be accessible for inspection. The installation requires a tightness test before commissioning (test pressure: min. 10 kPa for min. 30 minutes per PN-EN 1775).
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