Miele NOVOTRONIC T 1576 Operating Instructions Manual page 30

For best drying results, avoid extra long
ducting with too many bends or angles.
Avoid ducting in tight corners.
Use flexible metal pipe or rigid metal
pipe for venting. Non-metallic flexible
hose should not be used since it is a
potential fire hazard.
The shorter the exhaust ductwork, the
more efficient the dryer will be. Ex-
pelled 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 that will be
created.
An elbow or bend creates more friction
than a straight duct. An additional duct
length factor must therefore be added
for each elbow or bend (see Table 1.)
This factor expresses the restistance of
the bend in terms of a straight length of
duct.
The additional length factor is then
added to the measured duct length to
give the effective duct length.
A larger duct diameter helps to reduce
friction. The duct diameter should
therefore be increased with increasing
duct length.
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