A flush mounted hood in a 9-foot ceiling would have to encompass much of the ceiling to deal with the expansion of the rising effluent. Expansion can be up to 20 or more degrees half angle at the cooktop, and as the effluent rises, cools, and slows down, minor drafts will further disperse it. While there are commercial kitchen ventilation systems comprising perforated ceilings with high intensity UV grease conversion devices above them, this is not a direction I think you want to go.

And large ceiling hoods will require large air flow rates to keep the velocity up at the baffles. Such rates imply large external exhaust fans and similarly massive make-up air systems (unless the house is only a roof in Pago Pago.)

Aim for a hood that overlaps the cooking area by 3 or more inches on each side, and limit the gap from cooktop to hood aperture to 36 inches.

kas

I love our zephyr Genova. it's under cabinet I don't know exactly what flushmount is but it is a clean streamlined look.