District Heating Pipe Sizing Calculator
Nominal size from capacity, spread and pressure gradient
The calculator determines the nominal size of a single heat network pipe, such as a house connection or a distribution line. The mass flow follows from connection capacity and temperature spread; the tool selects the smallest nominal size per EN 253 that satisfies the allowable pressure gradient and the velocity limit.
Preliminary sizing of a single pipe — the tool selects the smallest nominal size that satisfies both the pressure-gradient and the velocity criterion.
- Mass flow
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- Volume flow
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- Velocity
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- Pressure gradient
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| DN | dᵢ (mm) | v (m/s) | R (Pa/m) | Criteria |
|---|---|---|---|---|
Assumptions: fluid properties at mean temperature — heating water at 70 °C (ρ = 978 kg/m³, cₚ = 4.19 kJ/(kg·K), ν = 0.41·10⁻⁶ m²/s); cold network at 10 °C: water (ρ = 1000 kg/m³, cₚ = 4.19 kJ/(kg·K), ν = 1.31·10⁻⁶ m²/s) or water-glycol 30 vol% (ρ = 1040 kg/m³, cₚ = 3.7 kJ/(kg·K), ν = 3.0·10⁻⁶ m²/s) · roughness k = 0.05 mm, inner diameters per EN 253 (steel service pipe) — an approximation for cold networks, where PE pipes are common · friction factor per Colebrook-White · velocity limits: house connection 1.0 m/s, distribution and cold networks 1.5 m/s, transmission 2.5 m/s. The tool provides a preliminary sizing and does not replace a hydraulic network calculation. Last updated: July 2026. VICUS Software accepts no liability for the correctness of the results.
How the calculator works
Connection capacity Q̇ and spread ΔT give the mass and volume flow, and from these the flow velocity for each nominal size:
ṁ = Q̇ / (cp · ΔT) V̇ = ṁ / ρ v = V̇ / (π · di² / 4)
The pressure gradient per metre of pipe is calculated with Darcy-Weisbach. The friction factor λ follows from the Colebrook-White equation in turbulent flow (roughness k = 0.05 mm) and from λ = 64/Re in laminar flow:
Re = v · di / ν R = (λ / di) · (ρ · v² / 2)
- Nominal sizes DN 20 to DN 500 are checked, with inner diameters per EN 253 (steel service pipe).
- The tool selects the smallest size with R ≤ Rmax and – if enabled – v ≤ vmax (house connection 1.0 m/s, distribution and cold networks 1.5 m/s, transmission 2.5 m/s).
- Fluid properties at mean temperature: heating water at 70 °C; for cold networks water or water-glycol 30 % at 10 °C.
- The result is a preliminary sizing per pipe. Simultaneity, network branching and the pressure profile to the critical consumer are not considered.
Background and theory
Guide values for pressure gradient and flow velocity, the background of both criteria and a worked example are covered in the knowledge article pipe sizing in district heating networks.
For a full thermo-hydraulic network simulation with annual load profiles, heat losses and pump energy for every pipe, use VICUS Districts.