Pressure and self-adjusting air inlet vents. The amount of air supplied depends on the pressure differences inside and outside the room. It happens until the capacity of the air inlet vent reaches the maximum value. When the pressure keeps on rising, the choke valves deflect to limit the amount of supplied air. Such situations may result from e.g. a blast of wind. The user has a chance to close the block in order to limit the flow of air to the minimum, that is about 5m3/h.