The ideal height for these fans is 10' from the ground so they would need to drop approx 15'. We sell 12, 18 and 24 inch down rods. Item includes a 6 inch down rod.

Keeping the blades at 10 feet from the floor would maximize the
perceived air flow while staying at the safe blade height prescribed by
UL. That would mean the customer would need a 14.5 foot long down rod.
There is a complication with the wiring when the down rod is extended
beyond four feet. The customer would need to add the additional length
of wire to the wiring of the fan to allow it to be installed.