In order to reduce the primary energy consumption of buildings, highly efficient heat recovery of the HVAC system is indispensable. A reduction of the fresh air rate is not advisable; Indoor Air Quality (IAQ) is essential for the health and wellbeing of the user. In order to nullify the additional pressure loss of the heat recovery unit a mechanical ventilation system is needed. Central ventilation systems have to incorporate an oversized and space-consuming low-loss ductwork system, decentralized ventilation systems use multiple decentralized ventilation units at the facade. Both kinds of systems must have one fan each for supply air and return/exhaust air. An innovative decentralized ventilation solution is presented that uses only one fan for both supply and exhaust. Mirroring the principle of “breathing”, this facade-mounted solution uses a damper system that ensures air reversal, while the direction and flow through the fan remain constant, minimizing power consumption. A unit provides high-efficiency heat recovery, in excess of 90%, based on the use of a regenerator. It also has to have a number of inbuilt control systems that react to the changes in the wind pressures on the façade, essential for use in multi-story buildings, and the ability to offer demand-based ventilation when the space is unoccupied. The first large-scale projects have shown that this ventilation technology is suitable to minimize the primary energy without compromising the IAQ, even in inner zones. Transient ventilation allows heat recovery without freezing even at very low outside temperatures, therefore no bypass is necessary, heat recovery is actively controlled through variations in the breathing cycle time and the air volume. The transient mode of the supply air has a positive influence on comfort in comparison with the steady-state mode achieved with constant or variable air supply.