A ground-source heat Pump (GSHP) model is formulated and used to estimate the potential of a domestic GSHP as a carbon-saving technology (compared to a conventional gas boiler) with actual thermal data for a dwelling in the UK. The model shows good agreement with current sizing guidelines but Shows possible barriers to the carbon-savings (and running cost savings) of GSHPs. This includes an analysis of output temperatures, system sizes and grid CO2 intensity. The model suggests that GSHPs should be aimed towards a new-build market (rather than retrofit) due to the likely reliance oil high Surface area/low temperature distribution systems. Also, grid CO2 intensity needs to be better understood when estimating the electrical consumption CO2 emissions of GSHPs, both for current and future scenarios. (C) 2008 Elsevier B.V. All rights reserved.