This paper presents different ventilation solutions for the retrofit in existing school building with a special focus on historic buildings. These building usually pose a major challenge for the integration of energy efficient ventilation systems, i.e. with heat recovery. For decentralized systems, the ductwork can be minimized by wall integrated heat recovery units, whereas for central systems, a horizontal air distribution in the attic combined with vertical ducts was found to be a possible solution for listed buildings. Former is problematic for aesthetic reasons due to visibility of the outer wall inlets, especially when no exterior insulation layer can be applied. A central unit with vertical ducts has the drawback of requiring many fire protection flaps, which are associated with high maintenance costs. Therefore a new ventilation system was designed and tested for a listed school building in Innsbruck (Austria), which is one of eight case study buildings within the EU-project 3ENCULT. In order to minimize the ductwork within the building, an active overflow system takes the air from the corridor to the class room and vents the extract air back to it. A central heat recovery system ventilates the staircase and the corridors with preheated fresh air. The prototype of the active overflow system, the control strategy and the simulation results are presented. To show the potential variants when implementing the active overflow principle, a further school building which will be energetically refurbished within the EU-project SINFONIA is presented. Here the HVAC-planning foresees the implementation of the active overflow concept with and without dedicated extract air ducting.