The performance of mechanical ventilation systems has been checked in several innovative residential houses as part of either a Swiss research or a P&D (pilot and demonstration) project. This paper gives a list of performance criteria for the ongoing comparison and evaluation of these mechanical ventilation systems. For some criteria, target Values are proposed. In the second part, this paper briefly describes four residential buildings with mechanical Ventilation systems where such evaluations were performed, and highlights interesting design features and results from the measurements. It then focuses on discrepancies between the design goals and what has been encountered in reality during the evaluation campaign. problem items were, among others, commissioning, occupant acceptance and window opening behaviour as well as sealing of ducts and heat exchangers.