Thermador recommends an additional inline backdraft damper for cold weather
installations. From page 4 of their installation manual:

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" he
http://www.luxurymetals.com/coppervents.html#anchor_423

A butterfly backdraft damper candidate is he
http://www.luxurymetals.com/butterfl...ft_damper.html

Don. www.donwiss.com (e-mail link at home page bottom).