Achieving current EU energy targets as stipulated in the energy service directive and in the energy strategy for 2020 implies substantial efficiency improvements across a variety of industrial end-uses. The achievable saving potential of an end-use depends considerably on the age structure of the existing stock and on the technology definition, i.e. whether a product approach, an extended product approach or a system-approach is used. Within this context, important ErP studies on air compressors are in preparation. In this paper, we address the possible contribution of compressed air systems to reaching Europe’s energy efficiency targets. Data availability is a limiting factor for such an analysis as information on the stock, type and performance of compressed air systems is only available to a limited extend. Therefore we suggest a “function-based” bottom-up stock-model. The basic idea of this modelling approach is to use the functional shape of proxy variables from available, official statistics with little additional technology-specific information rather than requiring a large set of detailed technology-specific data. The advantage of this modelling approach is to provide detailed results with only a limited number of assumptions that can be stated in a transparent manner. It facilitates the understanding of the effects of different efficiency improvements and allows modelling the impact of minimum energy performance standards. Using this kind of stock-modelling approach, we analyse the possible contribution of compressed air systems to the EU energy-efficiency targets, illustrating both the results of using different technology definition as stated above, but also pointing out major factors of uncertainty impacting on the results.