Air-source heat pump carbon footprints: HFC impacts and comparison to other heat sources

European governments see that heat pumps could reduce carbon emissions in space- and hot-water heating. EU’s Renewable Energy Directive designates heat pumps as renewable – eligible for various subsidies – if their carbon footprints are below an implied, average threshold. This threshold omits carbon generated by manufacture and emission of a heat-pump’s fluorocarbon refrigerant. It also omits the footprint of the heat pump’s hardware. To see if these omissions are significant, this study calculated carbon footprints of representative, residential heat pumps in the UK.Three findings emerged. First, in relation to power generation, which accounts for most of a heat-pump’s greenhouse-gas emissions, fluorocarbons add another 20% to the footprint. Second, at UK efficiencies a heat-pump footprint (in kg CO2e emitted per kWh delivered) is comparable or higher than footprints of gaseous fuels used in heating. It is lower than the footprint of heating oil and far lower than the footprints of solid fuels. Third, production and disposal of a heat pump’s hardware is relatively insignificant, accounting for only 2–3% of the overall heat-pump footprint. Sensitivities to the results were assessed: key factors are footprint of electricity generation, F-gas composition and leak rates and type of wall construction.