Highly efficient ventilation fans for exhausting air out from underneath roofs, and for being portable in use and application. The fan can include optimized airflow blades having a twisted configuration that can move at a rotational speed operation of up to approximately 500 rpm. The approximately 15 inch diameter twisted blades can be premolded on a hub that together form a single molded unit of plastic. They can also be fabricated using metal. The unit can be mounted in an exhaust outlet having a conical diffuser on or adjacent to a roof. Alternatively, the fan can be portable for use most anywhere there is a need for ventilation and moving of air. The blades can rotate by a solar powered motor, where the blades and motor can generate up to approximately 1040 cfm while using no more than approximately 16 Watts.