The heating transition in existing buildings: How transparency unlocks efficiency potential

The latest figures from the Federal Environment Agency (german only) highlight the challenge: emissions from the buildings sector rose by 3.4 million tonnes of CO₂ equivalents in 2025 compared with the previous year, reaching 103.4 million tonnes of CO₂ equivalents. Emissions also increased in the transport sector. With regard to the EU Climate Action Regulation, Germany’s cumulative total gap for the period 2021 to 2030 is projected to increase to 255 million tonnes of CO₂ equivalents. Buildings and transport remain particularly significant in this context. Part of the rise in emissions in the building sector is attributed to the cooler weather during the heating season. However, the figures also make it clear that energy efficiency in the existing building stock remains a key challenge. The question is therefore not only which technologies will be installed in future, but also how existing buildings can be operated more efficiently.

A key lever lies in the day-to-day operation of buildings. Heating systems do not always operate under optimal conditions. Consumption patterns often go undetected, deviations in system operation are only identified at a late stage, and existing efficiency potential is not fully utilised. To systematically tap into this potential, transparency regarding the actual condition and use of buildings is essential. Digital data infrastructure thus becomes a key prerequisite for the heating transition in the existing building stock.

Against this backdrop, the German Business Initiative for Energy Efficiency (DENEFF) (german only) takes a critical view of the Climate Protection Programme 2026. According to the association, the programme “falls significantly short of what is required in the buildings sector”. DENEFF points out that, whilst the programme does contain important measures – including an increase in federal funding for efficient heating networks, the continuation of federal funding for efficient buildings (BEG), and an announced federal law on the energy-efficient refurbishment of public buildings – the initiative still sees gaps in the measures to reduce emissions in the buildings sector. Among other things, it is critical of the fact that, in its view, the programme does not compensate for the requirements that are to be scaled back under the planned Building Modernisation Act.

Unlocking efficiency potential in building operations

Alongside new construction and refurbishment, another question is therefore gaining in importance: how can existing buildings be operated more efficiently? In many properties, the necessary information on the condition of systems, consumption patterns and operational deviations has so far been lacking. Heating systems often operate at settings that were established years ago. Hydraulic balancing is carried out, but is not subsequently monitored or adjusted on an ongoing basis. Added to this are changing usage patterns and weather-related factors. As a result, there is often a gap between the theoretical assumptions made during the design phase and actual operation. Even buildings with good energy performance indicators can therefore, in practice, consume more energy than expected.
The gap between theory and practice is often also a question of the data available. Without knowing how a heating system actually operates, it is difficult to identify potential for optimisation. Without comparative data, deviations are often only recognised at a late stage. As a result, opportunities for optimisation measures requiring only a small investment often remain untapped.

Digital infrastructure as a lever

Heating monitoring, adaptive control and adaptive hydraulic balancing have long been in practical use. They provide a continuous overview of building operations and lay the foundations for operating heating systems in a more demand-responsive manner. Buildings are thus no longer controlled exclusively via fixed settings, but can respond more effectively to weather conditions, usage and the condition of the system. Funding schemes and investment remain key components of the heating transition. At the same time, the question of how existing systems can be operated more efficiently is coming to the fore. The key to this often lies not only in the system technology itself, but also in its control and continuous optimisation. When is heat required? How is consumption trending? Where do deviations occur? And what measures can be derived from this? Low-cost measures can be particularly effective where there is transparency regarding building operations. This requires data – and the ability to derive concrete courses of action from it.

Interoperability as the foundation of a digital ecosystem

One fundamental insight is often underestimated in the debate on the heating transition: climate protection and energy efficiency in the existing building stock are rarely a matter of a single technology. What is crucial is the interaction between different systems and stakeholders. A smart thermostat solution such as ‘Smart Heating’ can only realise its full potential if it is coordinated with the heating system and existing control processes. Similarly, heating monitoring only delivers added value when the data collected is incorporated into decisions regarding maintenance, operational optimisation and investment. Interoperability thus becomes a key prerequisite for efficiency. Only when sensors, data platforms, control solutions and operational processes are interconnected does a digital ecosystem emerge that creates transparency and enables optimisation. The neighbourhood-based approach, which is highlighted in the latest position paper from the Roundtable on the Heat Transition (german only) as a key component of the transformation, also ultimately requires a robust database at building level. This is because cross-sector solutions can only realise their full potential if consumption, operational and system data are available and can be put to good use.

What matters now

Regardless of how the heating transition is ultimately shaped politically, housing companies face a specific challenge: systematically identifying and harnessing efficiency potential within their existing building stock. This requires reliable data on building operations, the ability to derive courses of action from this data, and processes through which optimisation measures can be implemented on an ongoing basis.

Climate protection targets in the buildings sector are ultimately achieved in individual buildings – through numerous operational decisions made during day-to-day management. Digital infrastructure provides the necessary transparency for this and forms the basis for a more efficient use of energy in the existing building stock.