Phasing out fossil fuel heating in UK homes: A multi-dimensional framework for sustainability assessment of alternatives and their lifecycle implications

Space and water heating in the UK building sector, accounting for nearly a quarter of energy consumption and carbon emissions, is still dominated by fossil fuels. This has led to growing concerns regarding the decarbonisation of heating sources, supply chains, and operations in the built environment. The UK government aims to accelerate heat decarbonisation by mass deployment of low-carbon building heating systems (BHSs). However, heat transition involves more than shifting to less carbon-intensive technologies. It is tightly interlinked with end-user livelihood and could have invasive spatial, social, and financial impacts on households and living spaces. Furthermore, substantial upgrades in building stock, infrastructure, energy market, and legislative frameworks are needed alongside the rollout of low-carbon alternatives. The multifaceted origins and complexity of the issue make it challenging to evaluate the potential of BHSs for serving a just and sustainable transition. This study proposes a life cycle sustainability assessment (LCSA) to evaluate the environmental, social, and economic impacts of alternatives, informing decision-making for more informed, effective, and accurately targeted interventions. Therefore, an integrated and purposebuilt LCSA framework is developed to evaluate BHSs' performance and lifetime implications at early project stages. This framework provides a sustainability-oriented decision support tool that expands current decision-making by proportional representation of all facets of sustainability and reflection of the stakeholders’ priorities. A mixed-method approach is utilised to identify 22 pivotal sustainability indicators (SIs) which can effectively represent the dynamic and complexity of BHSs. This is followed by developing consistent measurement methods and datasets to quantify the SIs. A new method accounts for fuel poverty as an SI is also developed, bringing this critical factor into preintervention decision-making. The sustainability assessment principles are then integrated with multi-criteria decision analysis (MCDA) techniques to build a practical LCSA tool which is applied to common individual BHSs for single-family UK houses, as a case study. Ultimately, results are validated through sensitivity analysis that explores the LCSA uncertainties and interdependencies between the SIs. The research argues that with climate change, economic uncertainty, and social inequity challenges, the need for holistic sustainability analysis of heating interventions is more evident than ever. A renewed focus on social sustainability is also needed as heating directly impacts households’ health, comfort, and well-being. In this context, environmental sustainability was found to be the most critical element (39. 5% of the overall sustainability weight), followed by the economic (33. 2%) and social (27. 3%) dimensions. The case study shows that no single BHS emerges as superior across all SIs. However, heat pumps (HPs) were the prominent technology in overall sustainability, with the ground-source form as the most promising option, followed by air-air and air-water HPs. The long-term benefits of HPs are highly reliant on the electricity:gas price ratio and the grid decarbonisation. Despite their increasing deployment, biomass boilers and direct electric systems were the least attractive options. The findings foster a better understanding of the sustainability challenges of heat transition, contributing to energy research, applied practices, and policy-making, towards a more sustainable future.