In 2012 I was called by Gearard who asked if I could install a 30 inch hall ceiling system he just bought at Orchard. I told him about the system in Yucaipa and he decided that was what he wanted. He and I both worked to install it and connect ducts to his 4 upstairs bedrooms. Again, this was a direct drive, not belted. When we turned it on it pulled a wind through his window that blew the curtains sideways.
Here is a picture of the central fan assembly. It has 2 18 inch duct collars. Those 2 18 inch ducts were connected to splitters that reduced each 18 inch duct to two 14 inch ducts for 2 rooms upstairs. So there were 4 total ceiling openings each 14 inches in diameter.
Gearard was delighted when he turned his new 6000 CFM system on and saw the wind (not a breeze) fly into his master bedroom window.