A meta-analysis of seasonal performance for ground to water and air to water heat pumps based on eight European trials for over 600 installations from five countries provides thirteen different descriptors of performance. Seven of these trials have previously been publish but no overview of their results has been attempted in terms of system boundary analysis. Trial boundaries are rationalised to four values of seasonal performance providing the opportunity to reassess the UK EST heat pump trial results and identify two boundary conditions directly relevant to the interpretation of the Renewable Energy Sources Directive. What is apparent is the wide range in performance at all boundaries and in all trials indicating that heat pumps are sensitive to design and installation practice. The overarching theme of the paper is the need for a unified framework for reporting heat pump performance and its applicability to the re-analysis of existing data. The task of building such a framework has proved beyond the present author, but the work presented here represents an attempt to scope the potential value and combination of analytical and practical difficulties that would need to be faced by those undertaking such a task. (C) 2013 Elsevier B.V. All rights reserved.