Network distribution heat loss and the CP1-style loss % KPI. Add one row per circuit segment
(custom bare/insulated pipe, or a manufacturer pre-insulated bonded pair).
Each segment's loss is the combined flow + return legs. Informational only. Always verify final design to project spec.
Loss % KPI mirrors DESNZ's Heat Network Optimisation Guide (2023) §5.3.2.2 model-validation formula. The good-practice/typical/high band is informational only: sourced from DECC's 2015 UK heat-network cost/performance survey (bulk-network average 6%, non-bulk average 28%), not a statutory pass/fail threshold. For design guidance only. Always verify with a qualified engineer.
About this heat network distribution loss calculator
This free heat network distribution loss calculator estimates the standing heat loss from a communal or district heating circuit and expresses it as the CP1-style loss percentage of annual delivered heat. You add one row per circuit segment, either a custom bare or insulated pipe, or a manufacturer pre-insulated bonded pair from the presets. And it sums the flow and return leg losses across the network. It is aimed at UK heat network and M&E designers assessing distribution efficiency at design stage. The loss physics follow BS 5422:2023 / CIBSE Guide C. Everything runs in your browser. Nothing is uploaded.
How the distribution loss is calculated
For a custom segment the per-metre loss is the series of a cylindrical conduction resistance and a surface-film resistance: Rcond = ln(r₂ ÷ r₁) ÷ (2πk) and Rs = 1 ÷ (h × 2πr₂), giving Q = ΔT ÷ (Rcond + Rs) per BS 5422:2023 / CIBSE Guide C. Run once for the flow leg and once for the return leg and summed. A pre-insulated bonded pair uses the manufacturer’s published W/m scaled linearly from its reference Δθ. The driving difference is Δθ = mean(flow, return) − ground/ambient. Annual energy loss is total W × operating hours ÷ 1000, and the loss % KPI is annual loss ÷ annual delivered heat, mirroring DESNZ’s Heat Network Optimisation Guide (2023). The good-practice / typical / high band is informational (DECC 2015 survey benchmarks), not a statutory pass/fail.
Frequently asked questions
Why count both the flow and return legs?
A heat network circulates hot water out on the flow and back on the return, and both pipes lose heat to their surroundings the whole time. Each segment’s loss is therefore the flow leg plus the return leg. The return still runs well above ground or ambient temperature, so it is a significant part of the total.
Custom pipe or pre-insulated pair?
Use a custom segment when you want to model a bare or site-insulated pipe from its outside diameter, insulation thickness and conductivity. Use a pre-insulated preset (Maincor/Logstor PexFlextra Twin or Uponor Ecoflex Thermo Twin) to take the manufacturer’s published W/m directly, scaled to your network temperatures, the usual choice for buried bonded-pair mains.
Is the loss % band a compliance check?
No. The loss % KPI itself mirrors the DESNZ Heat Network Optimisation Guide model-validation formula, but the good-practice/typical/high band is informational only, drawn from the DECC 2015 UK heat-network survey (bulk-network average around 6%, non-bulk around 28%). Treat it as a sense-check, not a statutory pass or fail.