„When you can’t buy it…“. A fan with a „drying“ function was not found on the market for the needs of permanent, controlled ventilation of damp spaces, where it was not possible to remove the cause of rising moisture through masonry. Permanent use of air dryers is expensive to operate, and uncontrolled, permanent air exchange with a fan is counterproductive in unsuitable climatic conditions and the humidity, for example during rain or high external relative humidity, paradoxically increases. After verification of the prototype, the fan solution with a drying function was registered with the Industrial Property Office and a manufacturer from the field of air conditioning showed interest in the protected solution and bought the solution.