Heat Loss Calculator for District Heating Pipes
Heat loss of buried pre-insulated pipes per EN 13941
The calculator determines the steady-state heat loss of a buried supply and return pipe pair made of pre-insulated bonded pipe per trench metre. Inputs are nominal size and insulation series per EN 253, the fluid and ground temperatures and the laying conditions; thermal coupling of two pipes in a shared trench is considered per EN 13941.
Steady-state heat loss of a buried pre-insulated pipe pair (supply and return) per EN 13941 — from nominal size, insulation series, temperatures and laying conditions.
- Supply
- –
- Return
- –
- Annual loss*
- –
- Insulation share of R
- –
| Layer | Ø (mm) | R (m·K/W) | Share |
|---|---|---|---|
| Steel pipe | ≈ 0 | – | |
| PUR insulation | |||
| PE casing | |||
| Soil | |||
| Total R per pipe | 100 % | ||
| Coupling R₁₂ | – |
Assumptions: steady-state calculation per EN 13941 with cylindrical thermal resistances in series · steel outer diameter d_a and casing outer diameter D_c per EN 253 (series 1/2/3, common standard dimensions), PE casing wall thickness per EN 253 (3.0–6.0 mm), λ_PE = 0.43 W/(m·K) · thermal resistance of the steel pipe neglected (< 0.1 % of R) · homogeneous soil, undisturbed temperature T₀ at pipe axis level, surface heat transfer not considered separately · coupling of two single pipes via R₁₂ (zero-order multipole approximation) · *annual loss = total × 8760 h — only valid for year-round operation at the entered temperatures; enter annual mean temperatures for an annual balance. Ageing of the PUR insulation (λ increasing over the service life) is not considered. Last updated: October 2026. VICUS Software accepts no liability for the correctness of the results.
How the calculator works
For each pipe, the thermal resistances of the cylindrical layers and of the soil are added in series (per metre of pipe). da is the outer diameter of the steel pipe, Di and Dc are the inner and outer diameter of the PE casing, h is the depth of the pipe axis:
RPUR = ln(Di / da) / (2π · λPUR) RPE = ln(Dc / Di) / (2π · λPE)
Rsoil = ln(2h/Dc + √((2h/Dc)² − 1)) / (2π · λsoil) R = RPUR + RPE + Rsoil
If supply and return lie side by side at centre distance s, they influence each other through the soil. The coupling resistance R12 leads to a coupled system of equations (T0: undisturbed ground temperature):
R12 = ln(√(1 + (2h/s)²)) / (2π · λsoil)
qs = [(Ts − T0) · R − (Tr − T0) · R12] / (R² − R12²)
qr = [(Tr − T0) · R − (Ts − T0) · R12] / (R² − R12²)
- Dimensions per EN 253: steel outer diameter per DN, casing outer diameter Dc per insulation series, PE wall thickness 3.0–6.0 mm; λPE = 0.43 W/(m·K). The resistance of the steel pipe is negligible.
- Without coupling (R12 = 0), each pipe is treated as a single pipe: q = ΔT / R.
- The annual loss is q · 8760 h and only applies if the entered temperatures persist all year. For an annual balance, enter annual mean values of supply, return and ground temperature.
- Check value: DN 80, series 2, λPUR = 0.027, h = 0.9 m, λsoil = 1.5, 90 °C against 10 °C gives q ≈ 18.7 W/m as a single pipe – about 92 % of the temperature difference drops across the insulation.
Background and theory
Influencing factors, typical loss shares of different network types and the estimation of annual heat losses are explained in the knowledge article heat loss calculation per EN 13941.
For a full thermo-hydraulic network simulation with annual load profiles, heat losses and pump energy for every pipe, use VICUS Districts.