Moisture Exhaust Ducts??

[Marc M]

Are they referring to condensation from the duct?

504.3 Clothes Dryers.
504.3.1 Moisture Exhaust Ducts. Moisture exhaust
ducts shall terminate on the outside of the building and
shall be equipped with a back-draft damper. Screens shall
not be installed at the duct termination. Ducts for
exhausting clothes dryers shall not be connected or
installed with sheet metal screws or other fasteners that
will obstruct the flow. Clothes dryer moisture exhaust
ducts shall not be connected to a gas vent connector, gas
vent, or chimney, and shall only serve clothes dryers.
Clothes dryer moisture exhaust ducts under positive pressure
shall not extend into or through ducts or plenums.

[Mike Kleisch]

As I read it, they are referring to the moist air created by the dryer, as it dries wet clothes, and exhausting it through ductwork to the great outdoors.

Another way to read 504.3.1 is:

The first two sentences could apply to any ductwork that exhausts moist air as a reference for other code sections, after that it pretty much talks about specifics for dryers.