Which is best a direct drive whole house fan or a belt driven whole house fan?

With a belt drive the fan speed can be easily raised or lowered but there is belt and bearing maintenance to consider (with a belt drive there are 2 additional bearings). With direct drive replacing the motor is a little more involved and blower size is limited. Other than that no difference. Determine which characteristics are more important to you and make your choice. On a furnace/AC unit, I would go with DD personally.