District Heating Network Inspection by Drone

District heating networks transport hot water or steam under pressure over several kilometres, often buried beneath roads and green spaces. A leak or insulation failure translates into significant heat losses — between 5 and 15% of produced heat in poorly maintained networks — without being visible at the surface. Aerial infrared thermography by drone detects these anomalies before they escalate into pipe failures.

How thermography detects losses in buried networks

Heat escaping from a failing pipe diffuses through the surrounding soil and rises to the surface. This thermal flux creates a heat signature at ground level, typically as a warm band above the pipe route, more pronounced at leak points or areas of degraded insulation.

This signature is captured by the drone's thermal camera during a night or early-morning flight, when the surface soil has cooled and the thermal differential between normal zones and warm zones is at its maximum.

The result: a thermal map of the network overlaid on the pipe layout plan, allowing precise localisation of loss zones without prior ground investigations.

Use cases and intervention contexts

Preventive maintenance of existing networks

For district heating operators (local authorities, urban heating companies), an annual or biennial aerial thermography campaign is the most effective monitoring tool for early detection of insulation degradation and planning pipe rehabilitation before failure occurs.

A 10-kilometre network can be inspected in a single night's flight, whereas a ground-level investigation would require several weeks of trenching and heat flux measurements.

Pre-rehabilitation assessment

Before launching a rehabilitation programme for an ageing network, aerial thermal mapping allows prioritisation of sections to be replaced according to their loss level. This prioritisation optimises the budget by targeting interventions with the greatest impact on network efficiency.

Post-incident diagnosis

In the event of unexplained pressure drops or abnormal increases in energy consumption, drone thermography enables rapid localisation of a leak without exploratory excavation.

Limitations and application conditions

Aerial thermography of buried networks is most effective in specific conditions:

• Burial depth — the deeper the pipe, the more attenuated the surface thermal signal. The method is optimal for depths below 1.5–2 metres
• Soil type — mineral surfaces (asphalt, concrete) transmit heat well; very wet soils or dense vegetation attenuate the signal
• Outdoor temperature — winter conditions (cold ground) maximise the thermal differential and improve detection
• Network load — the network must be in service (hot water circulating) at the time of the flight

Our field approach

We carry out heat network inspections with the DJI Matrice 4TD in thermal configuration, during night-time slots in winter or shoulder season to maximise signal quality. Thermal images are orthorectified and overlaid on the network plan for precise anomaly localisation.

Our inspection report indicates, for each detected anomaly, the GPS location, the likely nature of the anomaly (leak, insulation degradation, singular point) and the intervention priority level. The report is directly usable by network maintenance teams.