I'm needing to install a Nutone Allure III (model WS330WW, 430 CFM) under-cabinet range hood to vent vertically from the top panel (and NOT the rear panel) into 3.5"x10" rectangular ducting that then runs horizontally through some kitchen cabinets (see attached pic, please). Which of these two possible transitions should attach immediately to the top panel of the hood?
A. http://www.homedepot.com/p/Broan-3-1-4-in-x-10-in-to-7-in-Round-Galvanized-Steel-Silver-Duct-Transition-412H/202914175 ,
Will airflow be much smoother (less turbulence) if the air initially exits the hood through a 7" round opening, as opposed to a 3.5"x10" rectangular opening? Or, does round versus rectangular not matter since the cross-sectional area is almost the same i.e. 350 square inches?