Product review (3 stars): Poor engineering for ducted vent change over.
Spent a few hour on the prep and install to replace an old kenmore unit.  Well now I think the Kenmore unit may have performed better, but looked worn out and had no style.  This Broan unit ships prepped for non vented set up.  The change over to vented was easy, and the mounting was typical for a replacement - nothing is as easy as you plan.  Ha!  But the 1st time I tested the vent fan I noticed it is spilling a lot of air out the non vent port on top of the unit.  It should not be doing this at all!!!!  I took it apart and tried to reseal the plastic device that is supposed to block off  the non vent port - I found the plastic blocking device was seated properly.  Put it back together and its only a bit better - still spilling air out the non vent port that should be totally blocked off. The seal of the plastic duct for non-vented application must not be seated properly against the weather stripping on the underside of the hood top.  I guess I will have to disassemble again, and tape off the dang vent openings permanently with aluminum duct tape from the inside of the hood. Poor design - I say this unit is built for non-vented applications first.  I would have paid a bit more $$ for a unit that was dedicated to ducted ventilation only, though it would be cheaper for Broan to produce a unit without the non-venting plastic duct and punched vent holes in the top of the hood.