Empowering building owners for the heating transition: open-source tool simplifies DIN EN 12831 for low-temperature-ready assessment

Peer-reviewed paper 1-118-26

Accounting for roughly 35% of European GHG emissions, building sector is central to achieving GHG neutrality by 2050, particularly through heat decarbonisation and efficiency. Heat pumps (HPs) are well established in new buildings. In contrast, more than 70% of existing buildings rely on fossil fuels, although many of them could operate HPs efficiently. Key indicator for this is heating flow temperature, depending on room heat losses and radiator output. Replacing undersized radiators can often suffice to lower flow temperatures below 55°C at design conditions, corresponding to LT-ready as an indicator for efficient HPs.

Despite the high potential of HPs in existing buildings, uncertainty about suitability and costs remains a major barrier, as owners must decide before professional planning begins. To address this early-stage decision barrier, we present an open-source web application. It operationalises a simplified room-level heating load and radiator assessment, presented in structured and decision-oriented format, rather than providing binary pass/fail rating, focussing on actionable and affordable recommendations. By lowering informational and analytical barriers, it empowers building owners to assess HP-suitability, identify potential retrofit measures and engage more informed with professional planners.

A plausibility assessment against professional DIN EN 12831 calculations demonstrates high accuracy for standard floor rooms. For complex attic rooms, geometric approximations – introduced for limited input scope and usability – can lead to deviations of up to ±20%, where area uncertainty outweighs U-value uncertainty. A systematic comparison of U-values shows good overall consistency with practice, with selective refinements applied to the underlying database.