District heating is considered a key component of the heat transition, especially in urban areas. However, its actual efficiency depends on one often invisible factor: heat loss in district heating pipes.
While renewable energy sources and intelligent control systems are the focus of many debates, physical losses in network operation often remain under-examined. Yet they are highly relevant, both economically and ecologically. Heat losses are the silent cost and emission drivers of many district heating networks. And at the same time, they are one of the biggest factors for optimisation.
Modern piping systems and targeted operating strategies now offer the possibility of significantly reducing these losses - not just on paper, but measurably in the field. The prerequisite: a clear understanding of the loss mechanisms, sound calculations, and a systemic view of technical, economic, and regulatory interrelationships.
What this blog is about:
The focus is on one key insight: those who ignore heat loss are foregoing potential efficiency gains. Those who reduce it in a targeted manner not only increase the performance of their network, but also its resilience and cost-effectiveness.
District heating is efficient, but never loss-free. Every metre of pipe involves heat loss due to physical factors. This is not a fault, but an integral part of the system. The decisive factor is therefore not whether losses occur, but how large they are and how specifically they can be influenced.
The physical basis is clear: heat always flows from the warmer to the cooler medium. In district heating pipes, this means from the hot water or steam in the pipe to the ground. The speed and intensity of this heat flow is determined by several technical and environmental factors.
The physical heat flow
Heat loss in district heating pipes occurs primarily through heat conduction, followed by heat transfer to the ground (convection) and – in the case of near-surface installation – also through radiation effects. The greater the temperature difference between the medium and the environment, the stronger the flow. And the fewer barriers (e.g. insulation), the higher the loss.
Technical influencing factors
Heat losses in district heating networks are the result of complex interactions between physics, technology, and the environment. They cannot be completely avoided, but they can be influenced in a very targeted manner. Knowing these factors allows you to set the course for a low-loss network right from the planning stage and when selecting materials.
Pipe material
Steel is considered the standard in conventional district heating construction, but it has disadvantages. The high thermal conductivity of the metal results in significantly higher losses compared to modern plastic pipes. Polypropylene (PP-R) has a significantly lower thermal conductivity. In practice, the material advantage is enhanced by additional insulation effects.
Pipe diameter
A larger pipe inevitably has a larger surface area and therefore also a larger potential radiation area. Although pressure losses can be reduced by increasing the throughput, in terms of energy efficiency, smaller is often more efficient.
Insulation quality
This is the most powerful single lever in the system. While standard insulation provides solid basic protection, plus or plus-plus can achieve up to 45% lower loss values. The decisive factor here is not only the insulation thickness, but also the thermal conductivity of the insulation material (λ value).
Soil properties and installation depth
Heat transfer to the ground is not a constant factor. Moist soil conducts heat better than dry soil, and pipes laid flat lose more heat to surface layers, where temperatures fluctuate. Deeper installation can therefore make sense from an energy perspective, even if it is more complex in terms of construction.
Age and condition of the pipe
Loss values increase significantly over time, especially if insulation becomes damp, slips, or is damaged. Corrosion, material fatigue, and leaks further exacerbate the problem. Old networks are therefore not only maintenance-intensive, but also energy-inefficient.
Differences between main and distribution pipes
Not all pipes contribute equally to the total loss. Main pipes transport heat at high temperatures over relatively short distances, usually with larger cross-sections. Distribution networks, on the other hand, connect many decentralised transfer points and add up to considerable pipe lengths. Their role in heat loss is often underestimated, yet they can account for up to 50% of the total loss.
Heat losses are difficult to grasp: they make no noise, do not drip, and do not cause sudden failures. And that is precisely why they remain undetected in many networks for a long time. Even moderate losses per metre quickly add up to enormous amounts of energy and correspondingly high operating costs over the length of a network.
A look at typical loss values provides the basis for informed decisions. After all, only those who know how much heat is lost can take targeted countermeasures.
In practice, heat loss per metre of district heating pipe is expressed linearly as power loss per metre of pipe (W/m). This value depends on several factors:
| Pipe type and condition | Power loss (W/m) at 90/70 °C |
|
Old pipe (steel, standard insulation) |
35-50 |
|
Modern steel pipe, standard insulation |
25-35 |
|
Plastic pipe, plus insulation |
15-25 |
|
aquatherm energy twin with optimised insulation |
10-18 |
A loss of 25 W/m sounds moderate. But with a 1,000 m pipe, this value adds up to 25,000 W – i.e. 25 kW of continuous power loss. Over the course of a year (8,760 operating hours), this results in an energy loss of around 219,000 kWh or 219 MWh. By way of comparison, the average annual heat requirement of a single-family home is 12 to 20 MWh: the losses from a single pipe could therefore supply 10 to 15 households.
The DIN EN 13941 standard specifies the methodological standards for calculating heat losses in district heating networks. It is based on the Wallentén model and distinguishes between symmetric and antisymmetric losses, which are particularly relevant for TwinPipe systems. It also takes into account:
It is therefore worth doing the maths: knowing the loss values not only reveals energy weak points, but also quantifiable optimisation potential. The difference between an outdated network and a modern system often amounts to several hundred MWh per kilometre of pipeline per year.
Heat losses are the result of technical decisions and can be drastically reduced by measures that are both technically and economically sensible. The solution does not lie in a single product, but in a multidimensional optimisation approach: material selection, insulation standards, system architecture, and operational management must all work together. Only this interaction turns a district heating network into a truly efficient system.
Technological levers: what pipelines can achieve
High-quality insulation: the biggest lever per metre
Modern Plus or Plus-Plus insulation reduces heat loss by 20–45% compared to standard solutions. The decisive factors here are:
The investment often pays off faster than expected: for long routes and year-round operation, additional insulation costs are amortised within a few years.
Modern piping systems made of PP-R (e.g. aquatherm energy)
Plastic pipes based on polypropylene offer several advantages over steel:
Thermally superior: significantly lower thermal conductivity
Self-compensating: no expansion compensators required
Corrosion-free: no consequential damage from rust
Hydraulically efficient: smooth inner surfaces → lower pump requirements
Weight reduction: approx. 70% lighter than steel → faster and cheaper to install
Twin Pipe systems:
synergy of supply and return
Flow and return in a common jacket pipe not only reduce installation costs. They also reduce heat loss by up to 37%, as thermal effects influence each other and enhance the insulating effect.
Operational optimisation: efficiency in everyday use
Technology alone is not enough. Network operation must also be optimised to minimise heat loss. Three key levers:
Lower the flow temperature
Power loss increases in proportion to the temperature difference between the medium and the ground. Example: Reducing the flow temperature from 90 °C to 80 °C reduces heat loss by up to 20 %. Modern fourth-generation networks operate with flow temperatures of 60 to 70 °C – while maintaining the same level of supply reliability.
Optimise the return temperature
A low return temperature is doubly valuable: it not only reduces the absolute loss, but also increases the spread and therefore improves the efficiency of heat generation.
Possible measures: hydraulic balancing, optimised transfer stations, and smart control technology.
Leakage control and preventive maintenance
A gradual loss of water often also means a loss of heat, especially in the case of damp insulation. Modern leak detection systems, regular network checks, and targeted renovations prevent massive efficiency losses. The return on prevention is usually high in this case.
Network modernisation: when replacement is cheaper than maintenance
Older networks in particular often reach their technical limits. Insulation becomes damp, pipes are weakened by corrosion, and power losses are massive. In such cases, the structured replacement of entire sections of the network is worthwhile, especially if power losses exceed 40 W/m, repair costs are rising, or network conversions (e.g. due to new neighbourhoods) are planned. In many cases, the investment in modern systems pays for itself within 10 to 15 years – while simultaneously increasing operational reliability and flexibility.
Heat losses in district heating networks are not just a thermal phenomenon, they are also an economic factor. Every loss that is not avoided means higher fuel costs, greater generation capacities, and more CO₂ emissions. Operators who modernise and specifically optimise their networks secure significant, future-proof advantages.
This is because the lower the losses, the less energy needs to be provided at the point of generation. For example, a network with a feed-in capacity of 100 MW and a loss of 12% causes 10,500 MWh of energy loss per year. If this percentage is reduced to 8%, the demand is reduced by 3,500 MWh, which corresponds to an annual saving of 280,000 € at an average heat price of £80/MWh €. The effect is amplified by rising energy prices or decarbonisation targets that necessitate expensive alternative generation technologies.
Lower pumping requirements: Plastic pipes such as PP-R have smooth inner surfaces. The hydraulic resistance is lower than that of comparable steel pipes, which significantly reduces the energy required for pumping. In a typical urban network, this can save several tens of thousands of kWh of electricity per year.
Greater supply reliability: Corrosion, burst pipes, and gradual leaks are classic problems in older buildings. Plastic pipes are completely corrosion-free and retain their material integrity for decades. Fewer faults mean fewer repairs, less downtime, and greater customer satisfaction.
Flexibility for future requirements
Modern networks must be scalable and adaptable: new neighbourhoods, new heat sources, new operating modes. Modular systems such as aquatherm energy can be easily expanded, converted, or connected in a decentralised manner.
They are compatible with low-temperature concepts, paving the way for the fourth generation of district heating.
Climate impact: less loss = fewer emissions
Every kilowatt hour saved reduces emissions – regardless of the generation mix. The effect is particularly noticeable with fossil fuel heat carriers:
Efficiency is also increasing for renewable heat, which significantly improves the economic amortisation of solar thermal energy, geothermal energy, and waste heat utilisation.
Verifiability and monitoring
Efficiency gains through heat loss reduction can be verified. This can be done for internal stakeholders, local authorities, funding bodies, and certification bodies. This transparency is increasingly a prerequisite for access to funding and a strategic advantage in public tenders or municipal procurement. The appropriate means are:
Service life and investment security
Modern plastic systems offer a technically documented service life of 50 years and more – with minimal maintenance. This significantly reduces the total cost of ownership and reduces the risk of unplanned CAPEX expenditure.
District heating is a key technology in the heat transition. However, it is only as good as its implementation. Nowhere are structural weaknesses more evident than in heat loss within the network. What begins as a physical inevitability can quickly become an economic risk: losses that are permanently accepted are wasted energy and wasted capital.
The analysis clearly shows that heat losses are technically explainable and quantifiable. They can be massively reduced through modern materials, insulation concepts, and operational management. The economic, energy, and ecological effects are measurable and effective in the long term.
Against this backdrop, modern plastic pipe systems such as aquatherm energy offer a clear differentiating feature in the construction of efficient district heating networks. Thanks to their low thermal conductivity, they actively contribute to reducing pipe losses. At the same time, they enable permanently high insulation standards that remain stable even under real operating conditions. The systems are easy to install, which reduces time and costs during construction – especially in renovation projects or in densely built-up areas. During operation, they score points for low maintenance costs and high operational reliability, as they are completely corrosion-free. Added to this is their modular expandability: pipes, fittings, and accessories can be flexibly adapted to individual requirements.
Next step: individually assess potential.
Every district heating network has its own specific conditions – but the key questions are always the same: How high are the current heat losses? Which technical measures will have the greatest effect? And how can the network be made efficient, economical, and climate-compatible in the long term?
aquatherm supports operators and planners as a solution partner: with technical expertise, tried-and-tested system solutions, and a holistic view of economic feasibility. Whether it's a new build, renovation, or targeted optimisation: the right solution starts with a well-founded overview.
Talk to our experts.
