Gas pipes follow their own sizing rules: gas velocity affects flow noise and pressure drop, while DVGW TRGI 2018 simultaneously sets limits on flow pressure at appliance connections. The gas pipe sizing calculator computes the minimum internal diameter required and assigns it to a pipe nominal size — for low-pressure household networks as well as medium-pressure lines in commercial installations.
Step by Step: How to Use the Gas Pipe Sizing Calculator
- Select the pressure range: Low-pressure network (below 100 mbar, typical house connection) or medium pressure (100 mbar to 1 bar). The pressure range determines the permissible maximum velocity.
- Enter gas type and standard volume flow: Add up all connected appliances — boiler 2.4 Nm³/h + cooker 0.5 Nm³/h + water heater 1.5 Nm³/h = 4.4 Nm³/h total demand. Diversity factors can reduce this value.
- Select flow velocity: Low-pressure lines: 3–5 m/s recommended. Above 5 m/s, audible flow noise occurs in low-pressure domestic pipes.
- Enter operating pressure for correction: At elevated pressure, the operating volume flow is smaller than the standard volume flow — the calculator automatically applies the pressure ratio correction.
- Read the nominal size: The result is the minimum internal diameter; then select the next larger pipe nominal size (DN15, DN20, DN25, DN32) and verify the pressure drop separately.
Practical Examples
Example 1 – Single-family home house connection: Boiler 24 kW (2.4 Nm³/h) + gas cooker 8 kW (0.8 Nm³/h) = 3.2 Nm³/h. At v = 3 m/s low-pressure: D = √(4 × 0.000889 / (π × 3)) = 19.4 mm → select DN20.
Example 2 – Commercial burner: 100 kW natural gas burner = 10 Nm³/h. At medium pressure 200 mbar, v = 10 m/s: operating volume flow = 10 × (1013 / 1213) = 8.3 m³/h → D = 17.2 mm → DN20.
Example 3 – Propane system at a campsite: 20 pitches each with 1.5 kW simultaneously = 30 kW propane → 1.16 Nm³/h. DN15 copper pipe from regulator at 3 m/s is sufficient for runs up to 10 m.
Gas Pipe Nominal Size Calculation
Maximum gas velocity: low-pressure lines 3–5 m/s; medium-pressure lines 5–15 m/s. Formula: D = √(4 × Q_norm / (π × v × pressure ratio)). House connection 5 m³/h at 3 m/s → DN20 is sufficient.
Frequently Asked Questions (FAQ)
Do I still need to check pressure drop after the velocity calculation?
Yes, always. The velocity method is only a first step. The pressure drop must then be calculated using the Darcy-Weisbach equation (use the gas pipe pressure drop calculator) to ensure the DVGW limit of 1 mbar in the low-pressure network is safely maintained.
What is a diversity factor in gas installations?
Not all appliances run simultaneously at full load. For more than 3 consumers, DVGW TRGI 2018 allows a reduced diversity value. Example: 5 appliances at 1 kW each → diversity factor 0.75 → sizing for only 3.75 kW instead of 5 kW.
Am I allowed to plan and carry out gas installations myself?
Planning and calculation are permitted and useful for preparation. However, installation in Germany is reserved exclusively for licensed contractors registered with the gas network operator.
