If you've got a really large space that needs a more efficient way to stay cool in summer and warm in winter, then Big Ass Fans ($TBD) are for you. These high volume, low speed ceiling fans are truly ginormous, ranging in size from 6 to 24 feet in diameter (now you know where their name comes from). One 24' fan can cool a 20,000 sq. ft. space on its own, using in-line helical gear reducers for nearly frictionless power transmission. These giants are engineered to move air without noise or wasted energy, providing over 25 times the airflow of a standard industrial ceiling fan.