The ceramic element does not have to be replaced during normal use, filters are available. The device can also be dismantled and cleaned after assembly. CYCLE I. The warm exhaust air is extracted from the room via the ceramic heat accumulator. The exhaust air heats and humidifies the heat accumulator. This transfers up to 90% of the thermal energy. After a while, the heat storage tank is heated up and the ventilation system switches to supply air mode. CYCLE II. The fresh, cold outside air flows over the heat accumulator and removes the stored heat and moisture from the heat accumulator until room temperature is reached. When the heat storage tank is cooled down, the ventilation system switches back to exhaust air mode. The cycle starts again. The switchover to the supply and exhaust air m.