This paper presents a novel method to analyse policy performance, using the example of legislation in the UK to require domestic boilers fitted since 1 April 2005 to be condensing. A technological uptake model based on the logistic equation is combined with four physical and economic models; Bayesian techniques are used for data analysis. Projections of energy savings are presented and the impact of different policy implementation dates investigated. Boiler efficiency is estimated to improve by a factor of 1.25 +/- 0.15 on replacing a conventional with a condensing boiler. Estimated savings of the policy are 176, 000(-127,000)(+86,000) GW h (or 32(-23)(+16) MTons of CO2e) between introduction in 2005 and 2013. Total estimated savings by 2050 of introducing the legislation in 2005 are 2, 000, 0001(-1,5,00,000)(+1,000,000) GW h (or 368(-276)(+184) MTons of CO2e), approximately 5.6 times the average annual domestic UK emissions from domestic gas use of approximately 66 +/- 5 MTons of CO2e. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).