How To Calculate The Effective Duct Length - Miele PT 7136 Plus User Manual

How to calculate the effective
duct length
The overall duct length will determine
the duct diameter.
^ Measure the actual duct length
needed to go from the dryer's
exhaust connection to the vent outlet:
1. Establish the number of elbows or
bends necessary, noting the type of
bend, angle and radius involved
(see Table).
2. Add the additional duct length (as
derived by using the values
specified in the table) and the actual
duct length to get the effective
length.
Note:
Maximum effective duct lengths:
4" (100 mm) diameter
5" (125 mm) diameter
6" (150 mm) diameter
Using the ring adapter up to an
effective duct length of 33 ft (10 m) and
a standard duct diameter of 4"
(100 mm) will provide optimal drying
times and energy consumption.
Do not use the ring adapter if the
effective duct length is more than 33 ft
(10 m).
Effective duct lengths over 66 ft (20 m)
require a larger duct diameter.
Longer ducts may lead to slight
decreases in dryer efficiency if the
necessary duct diameter is not
employed.
Installation of exhaust venting
66 ft (20 m)
132 ft (40 m)
328 ft (100 m)
Tips about the ductwork
– Check with your local building code
to determine the maximum allowable
duct length.
– Use a flexible metal pipe or rigid a
metal pipe for venting. Non-metallic
flexible hose should not be used, it is
a potential fire hazard.
– Use the wall vent or window
connection (optional accessories) for
venting outdoors.
– For optimal drying results avoid long
ducting with too many bends, angles
or tight corners.
– The shorter the exhaust ductwork,
the more efficient the dryer will be.
Expelled air is slowed down in the
ducts due to friction against the inner
walls. The shorter and smoother the
inner walls are, the less friction will
be created.
– An elbow or bend creates more
friction than a straight duct. An
additional duct length factor must be
added for each elbow or bend (see
Table). This factor expresses the
resistance of the bend in terms of a
straight length of duct.
The additional length factor is then
added to the existing duct to give the
effective length.
A larger duct diameter helps reduce
friction. Therefore the duct diameter
and length should be increased
simultaneously.
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