CP1-style diversified peak sizing for a heat-network riser/branch. Add one row per dwelling group
(instantaneous HIU or storage HIU) and get a diversified kW figure for each.
Diversity: DS439 coincidence curve (DHW, instantaneous) + Varme Ståbi rule of thumb (space heating). Not a substitute for full network hydraulic design.
Totals sum diversified figures across groups (no further network-level re-diversification, full hydraulic design is out of scope). For design guidance only. Always verify with a qualified engineer.
About this heat network diversity calculator
This free heat network DHW and space-heating diversity calculator works out the diversified peak load, in kW, for a communal or district heating riser or branch. You add one row per dwelling group, each on an instantaneous or a storage HIU (heat interface unit). And it returns a diversified figure per group and for the whole network, along with the diversity saving against the undiversified total. It follows the CIBSE CP1 approach: the Danish DS439 coincidence curve for instantaneous DHW and CP1’s own rule of thumb for space heating. It is aimed at UK heat network and M&E designers sizing risers at concept and tender stage. Everything runs in your browser. Nothing is uploaded.
How the diversified load is calculated
Space-heating diversity uses CIBSE CP1’s rule of thumb, diversity factor = 0.62 + 0.38 ÷ N for N dwellings. For instantaneous-HIU DHW, each dwelling is scaled to equivalent standard units (equivalent units = N × peak DHW per dwelling ÷ 37.6 kW, the DS439 standard flat peak) and the diversified load is read from the DS439 coincidence-factor curve, log-log interpolated between tabulated tiers. Storage-HIU groups have no published UK diversity curve, so their DHW load is the recovery duty Q = m × cp × ΔT over the recovery period (stored temperature to HSE L8/ACOP), summed conservatively without any diversity reduction. Group figures are then summed for the network total; there is no further network-level re-diversification.
Frequently asked questions
What diversity does the DS439 curve give?
DS439 is the Danish standard coincidence curve used across UK heat networks (here via the Mibec HIPER II design guide). It reflects the low probability that many dwellings draw hot water at the same instant, so the diversified DHW peak for a large block is far below the simple sum of every HIU’s rating, the more dwellings, the greater the saving.
Why is there no diversity for storage HIUs?
No citable UK diversity curve exists for storage-fed dwelling groups, so the calculator sizes them on conservative recovery-duty physics (Q = m·cp·ΔT over the recovery period) and sums them without a coincidence reduction. A note in the results flags this whenever a storage group is present, so the figure is honest rather than optimistic.
Instantaneous or storage HIU. Which do I pick?
Choose instantaneous for HIUs with a plate heat exchanger that make hot water on demand (the usual UK arrangement, which benefits from DS439 diversity), and storage for HIUs with a local cylinder charged over a recovery period. The choice changes both the DHW method and how much diversity is applied.