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Calculating the effective duct
length :
Friction against the inner walls of the
ducting will slow down the expelled air
as it passes through. An elbow, bend,
non-return flap or wall vent creates
more friction than a straight duct. The
friction created by each of these is
expressed as an additional duct
length factor. The additional length
factors are calculated by comparing the
friction created by, for example, an
elbow to that created by 1 metre of
straight plastic piping (Table I).
The additional duct length factor for
each item needs to be added together
to ascertain the effective duct length
required.
A larger internal duct diameter also
helps reduce friction. If the effective
duct length is more than 20 m the
duct diameter should be increased
(Table II).
1. To calculate the effective duct
length required:
^
First measure the distance which will
require straight ducting
. Multiply this
amount by the corresponding
additional duct length factor in Table I.
^
Establish the number of angles,
bends etc. necessary and add their
additional duct length factors
together with the help of Table I.
^
Add all the additional duct length
factors together to get the effective
duct length.
2. Internal duct diameter
^
Refer to Table II for the appropriate
duct diameter required.
Table I
Additional
duct length
factor
Flexible ducting*
–
1 m laid straight
–
45° angle
(Bend radius = 0.25 m)
–
90° angle
(Bend radius = 0.25 m)
1. 8 m
1. 5 m
2.5 m
Flexible aluminium vent hose* / plastic
piping
–
1 m laid straight / or 1 m
straight pipe
–
45° angle / elbow
(Bend radius = 0.25 m)
–
90° angle / elbow
(Bend radius = 0.25 m)
1. 0 m
0.6 m
0.8 m
Wall vent kit* or window vent kit*
–
with louvred grille
–
with non-return flap (hinged
flap)
3.8 m
1. 5 m
Non-return flap* to be
integrated into the vent
ducting
14.3 m
Flat ducting (for washer dryer
stack)*
11.0 m
Venting connection to the
left/right
1. 0 m
*optional accessory from Miele
Table II
Maximum effective
duct length allowable
Internal duct
diameter required
20 m
40 m
100 m
100 mm
125 mm
150 mm
Installation - venting
36