An investigation of the performance of a recently built estate of over 50 low-energy rental dwellings indicated that there was a slight but significant increase in electricity use of the “super low energy” designs over the control “low energy” designs. The “super low energy” designs included, in addition to the enhanced fabric specification of the “low-energy” types, active systems such as mechanical ventilation, solar DHW panels and enhanced space heating systems. While field monitoring indicated that the increased electrical energy usage was attributable equally to all the active energy systems installed, the occupants of these dwellings identified only the permanent mechanical background ventilation system as having a key energy cost. This perception was such that a number of occupants had attempted to disable or disconnect the ventilation system. This reaction to the perception of high running costs is of concern, not only in terms of possible impact on health and safety issues for the occupants, but also of maintenance issues for the estate operators.