In this dataset, a record qualifies if its title, abstract or claims combine district heating network or grid language with a specific fourth-generation concept such as supply temperature reduction, return temperature management, prosumer connection, hydraulic decoupling or heat loss ratio. This excludes generic heating equipment patents that do not address the network-level, low-temperature operating model. The 342 records in scope were filtered on that combined basis, not on keyword presence alone.

The ranking covers 61 companies, with the leading assignee holding 81 records versus 14 at fifth place and 10 at tenth place, so filing activity concentrates sharply at the top before spreading into a long tail. The top five assignees combined account for 53.2% of all 342 records in scope, while the top ten reach 69.3%. This is not a top-50 or top-100 list; it is the full ranked field the dataset returns.

Filings peaked at 58 in 2017 and, across the last comparable complete-year window, fell from 27 in 2021 to 17 in 2024, a -37% change. Figures for 2025 and 2026 appear lower still, but that reflects publication lag of roughly 18 months rather than an actual continued drop, since not all filings from those years have published yet. The honest read is a real slowdown through 2024, with the most recent two years still an open question.

F24D, covering domestic heating systems, appears in 62.3% of the 342 records and represents the densest claim territory, largely substation and pipework design. Control-related classes such as G05D (13.7%) and administrative filings under G06Q (7.3%) are smaller but present, suggesting network control logic and tariff or billing mechanisms are less crowded than core hardware. Areas like prosumer feed-in metering and return-temperature-based tariff design show lighter documented claim density and are worth a freedom-to-operate check before assuming they are occupied.

The most-cited records in this dataset, including WO2008039065A1 and WO2010102626A2, carry high citation counts partly because they are older and have had more years to accumulate references within the searched corpus. That makes citation count a useful signal of historical influence on how the field's claim language developed, but not a direct measure of which technology is most relevant today. Newer filings addressing control-layer or prosumer-specific claims may be technically more current despite lower citation counts.