Abstract: Well-designed and properly implemented Building Automation and Control Systems (BACS) can contribute to a reduction of the energy consumption in buildings, while increasing comfort and convenience for the occupants. For design and planning purposes, there is a need to quantify the potential impacts of implementing BACS, especially related to their capability for reducing the operational energy demand of a building. The simplified BAC factor method defined in standard EN 15232 aims to provide a generic estimation of expected energy savings. Alternatively, dynamic energy performance simulations can provide more detailed insights on a particular building design. Comparing energy savings from BACS in different sources in literature reveals significant discrepancies between various studies and assessment methods. This paper aims to clarify and discuss the differences between the various assessments and to identify the parameters that could affect BACS (i.e. heating, domestic hot water supply, lighting and shading control systems) performance in residential buildings. It is concluded that simplified methods as the EN 15232 BAC factor method do not provide a reliable estimate of achievable energy savings. The results obtained by more detailed simulations reported in literature show a significant variation in BACS performance. Two main causes are identified. Factors such as building and installation design parameters, occupant behaviour, context (e.g. climate) and baseline energy demand affect the energy saving potential but are not explicitly taken into account in the BAC factor method. Next, a significant part of the variation in reported energy saving potential can be attributed to discrepancies in modelling methods.