COLD WEATHER installations should have an additional backdraft damper installed to minimize backward cold air flow and a nonmetallic thermal break to minimize conduction of outside temperatures as part of the ductwork. The damper should be on the cold air side of the thermal break. The break should be as close as possible to where the ducting enters the heated portion of the house.
Now from reading this it appears that this is in addition to the damper that will be on the wall cap. I would think that Brooklyn qualifies as a cold weather installation.
Do people here think having two dampers makes sense? It will restrict the air flow some, though the fan currently spec'd is 1,000 CFM, which should be ample.
The wall cap I plan to use is the 10" here: http://www.luxurymetals.com/coppervents.html#anchor_423
A butterfly backdraft damper candidate is here: http://www.luxurymetals.com/butterfly_backdraft_damper.html
Don. www.donwiss.com (e-mail link at home page bottom).