The Fox up ventilation unit is a decentralised ventilation system for controlled room ventilation with heat recovery. The use of several units in pairs allows entire housing units / buildings to be ventilated. If operated with heat recovery, the ventilation unit works in 2 set time intervals. In the first interval (extraction phase), the “used” air in the room is sucked into the ventilation unit by the fan and carried to the outside. During this process, the air flows through the ceramic heat accumulator inside the ventilation unit, which extracts the heat from the air and stores it. In the second interval (delivery phase), “fresh” outside air is sucked in via the ventilation unit’s exterior opening. It passes through the unit, and is heated by the heat accumulator before entering the room. In this way, up to 90% of the heat contained in the extracted air can be transferred to the fresh air fed into the room. The principle of recharging and discharging a heat accumulator is referred to as regenerative heat transfer. When a single unit is used, an overpressure (delivery phase) or underpressure (extraction phase) is created in the room being ventilated depending on the operating phase. To guarantee a balance between the volumes of air delivered and extracted, it is recommended that Fox up units be used in pairs. The control of the ventilation units allows up to three pairs of units to be operated simultaneously.