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• Environmental life cycle impacts are assessed for current and future heating. • Electric air source heat pumps are the lowest-impact option to decarbonise heating. • Boilers using H 2 from natural gas with carbon capture cannot achieve Net Zero. • Boilers using hydrogen from electrolysis have the highest impacts in 17 categories. • The proposed 2050 Net Zero heating mixes reduce GHG emissions by 84–94% per kWh. Heating and hot water within buildings account for almost a quarter of global energy consumption. Approximately 90% of this heat is derived directly from the combustion of fossil fuels, primarily natural gas, leading to the unabated emission of carbon dioxide. This paper assesses the environmental sustainability of a range of heating technologies and scenarios on a life cycle basis. The major technologies considered are natural gas boilers, air source heat pumps, hydrogen boilers and direct electric heaters. The scenarios use the UK as an example due to its status as a major economy with a legally-binding net-zero carbon target for 2050; they consider plausible future electricity and natural gas mixes, including the potential growth of domestic shale gas. The environmental impacts are estimated using ReCiPe 2016. Current gas boilers have a climate change impact of 220 g CO 2 eq./kWh of heat, which could fall to 64 g CO 2 eq./kWh for boilers fuelled by hydrogen derived from natural gas with carbon capture. Heat from electric air source heat pumps or hydrogen from electrolysis can achieve net zero with a decarbonised electricity mix, but electrolysis has the highest energy demand of all options which leads to the highest impacts across 17 of the 19 categories. Despite their high carbon emissions, gas boilers remain the lowest impact option across 12 categories as they avoid the impacts related to electricity generation, including metal depletion, toxicities and eutrophication. By 2050, the best performing scenario sees the climate change impact of the heating mix fall by 95%; this is achieved by prioritising electric air source heat pumps without hydrofluorocarbon refrigerants, alongside demand reduction. The results show that, if infrastructure and financial challenges can be overcome, there are several viable decarbonisation strategies for heating, with heat pumps offering the most environmentally sustainable option of those considered here. However, increased renewable electricity demand may worsen some environmental impacts compared to natural gas boilers. [ABSTRACT FROM AUTHOR]