M1502.2 Concerning Duct Terminations: Exhaust ducts shall terminate on the
outside of the building or shall be in accordance with the dryer manufacturer’s
installation instructions. Exhaust duct terminations shall not be less than 3 feet in any
direction from openings into buildings. Furthermore, exhaust duct terminations shall
be equipped with a backdraft damper. Screens shall not be installed at the duct
M1502.3 Concerning Duct Sizes: The diameter of the exhaust duct shall be as
required by the clothes dryer’s listing and installation instructions.
M1502.4 Concerning Transition Ducts or Flex Hoses: Transition ducts shall not
be concealed within construction. Flexible transition ducts used to connect the dryer
to the exhaust duct system shall be limited to single lengths not to exceed 8 feet and
shall be listed and labeled in accordance with UL2158A.
M1502.5 Concerning Duct Construction: Exhaust ducts shall be constructed of
minimum .016 inches (0.4mm) rigid metal ducts, having smooth interior surfaces,
with joints running in the direction of air flow. Exhaust ducts shall not be connected
with sheet metal screws for fastening.
M1502.6 Concerning Duct Lengths: The maximum length of a clothes dryer
exhaust duct shall not exceed 25 feet from the dryer location to the wall or roof
termination. Additionally, the maximum length of the duct shall be reduced 2.5 feet
for each 45 degree bend, and 5 feet for each 90 degree bend. Finally, the maximum
length of the exhaust duct does not include the transition duct.