Whilst there is a broad consensus that energy efficiency as measured by the environmental performance certificates leads to higher asking rents, there is little evidence about investment strategies that consider energy efficiency as an optimisation factor. This paper focusses on identifying the conditions that lead to the highest increase in the willingness to pay for energy-conscious refurbishment. By making use of more than 1.5 m observations in Germany and the UK we disaggregate the expected willingness to pay to spatial, socioeconomic, and hedonic characteristics via Generalized Additive Models (GAMs). In a simulation study, we show that an investment strategy in residential real estate can be optimised via intelligent asset selection considering energy efficiency as an optimisation factor.