Built-in device with heat recovery for the ventilation of individual rooms. Aluminum plate heat exchanger with an efficiency of over 70%. State-of-the-art EC motors with the highest efficiency for extremely low energy consumption., Device unit with 4 power levels as well as exhaust and supply air operation and inner facade made of high-quality plastic., Fan housing (material: EPP) with 2 highly efficient, energy-saving direct current EC fans, two electric stainless steel external closure flaps with fly screens seal airtight to the outside when not in use. In the event of a power interruption such as a power failure, the flaps open automatically. Large-area aluminum plate heat exchanger with an efficiency of over 70%. Two efficient air filters made of class G4 electrostatic material in the supply and exhaust air flow guarantee the best air purity. An F7 pollen filter (accessory: item no. 9446) can be used as an option on the supply air side. The condensate is drained outside directly via the outer cover including drip tray. Power control via supplied KWL BCU control element including weekly timer and extensive functions. ,