I need to convert a range hood that is venting both up the vertical duct and into the room, to just venting up to the duct. In the photo, the room vent is seen on top of the hood.

http://www.nutone.com/common/seriesi...b-9600eae64e73

I have looked inside at all angles, and the squirrel cage fan is plenty strong enough to vent only up the duct. There is an assembly connected between the outlet of the fan to the top of the hood that directs some flow through the vent in the top of the hood into the room. But I don't see any way to close it - at least without taking things apart. No manual and searching the series number turned up nothing at www.broan.com.

Seems odd to me, but in any case, anyone ever seen this type of setup before?

Info from mfr plate:
Broan Allur Model QS1 Rev E, Mfd 2006, 1.8A, Hi/Low 110/220 CFM

Thanks buddies!