Excessive pressure drop in a gas pipe shows up as unsteady flames, ignition failures, or reduced heating output on cold winter days. The gas pipe pressure drop calculator uses the Darcy-Weisbach equation to check whether your pipe diameter is adequate for the planned flow rate — and thereby fulfils the verification requirement under DVGW TRGI 2018.
Step by Step: How to Use the Gas Pipe Pressure Drop Calculator
- Select gas type and density: Natural gas ρ ≈ 0.72 kg/m³, propane ρ ≈ 1.97 kg/m³ (at standard conditions). Propane has more than twice the density — this significantly increases pressure drop for the same pipe.
- Enter pipe diameter and material: Select the nominal diameter (DN) and material. PE pipe roughness 0.007 mm, steel pipe 0.046 mm, copper pipe 0.0015 mm — smoother surfaces generate less friction.
- Enter the pipe length: Total length from the pressure regulator to the appliance connection; add equivalent lengths for bends (approx. 1 m per 90° elbow at DN20).
- Enter the volume flow: Operating volume flow of all appliances running simultaneously, in m³/h.
- Check the result: In a low-pressure network, the flow pressure at the last appliance connection must be at least 17 mbar; the pressure drop from the house connection to the appliance must not exceed 1 mbar.
Practical Examples
Example 1 – Single-family home, natural gas: Boiler 24 kW + gas cooker 8 kW = 32 kW total → 3.2 Nm³/h operating flow. DN20 steel pipe, 12 m length: Δp = 0.65 mbar → below 1 mbar, sizing is correct.
Example 2 – Boiler too far from meter: 18 kW boiler, 22 m of DN15 copper pipe from the house connection. Result: Δp = 1.4 mbar → limit exceeded! Solution: use DN20 → Δp = 0.3 mbar.
Example 3 – Propane system in a holiday apartment: Gas cooker 4 kW + heating 12 kW on propane, 8 m DN25 PE pipe from regulator. Despite propane's higher density, DN25 yields only Δp = 0.22 mbar — well within limits.
Pressure Drop in Gas Pipes
Darcy-Weisbach formula: Δp = λ × (L/D) × (ρ × v²/2). Low-pressure gas network: max. inlet pressure 23 mbar, max. permissible pressure drop 1 mbar. Pipe material determines roughness λ: PE 0.007 mm, steel 0.046 mm.
Frequently Asked Questions (FAQ)
How do I account for bends and fittings in the pressure drop?
Every fitting adds resistance. As a rule of thumb, add an equivalent length of approximately 1 m (DN20) to 2 m (DN32) per 90° elbow. Isolation valves correspond to 2–5 m equivalent length depending on design; full-bore ball valves are significantly more favourable.
What is the difference between low pressure and medium pressure?
The low-pressure network delivers gas to domestic premises at a maximum of 23 mbar (typically 18–22 mbar). In medium-pressure networks (100 mbar to 1 bar), higher pressure drops per metre are permissible — depending on network level, up to 50 mbar may occur.
Is the pressure drop verification legally required?
Under DVGW TRGI 2018, proof of adequate flow pressure at the appliance connection is a mandatory part of the installation documentation that must be submitted to the gas network operator.
