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Calculating the effective duct
length:
Friction against the inner walls of the
vent duct will slow down the expelled
air as it passes through the duct. An el
-
bow, 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
length factor. The additional length
factors are calculated by comparing
the friction created by, for example, an
elbow to that created by 1 meter 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
which will be needed for the venting
system.
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 (Ta-
ble II).
1. To calculate the effective duct
length:
^
First measure the distance which will
require straight ducting
. Multiply this
amount by the corresponding addi
-
tional duct length factor in Table I.
^
Establish the number of angles,
bends etc. necessary and add their
additional duct length factors to
-
gether with the help of Table I.
^
Add all the additional duct length fac
-
tors together to give the effective
duct length.
2. Internal duct diameter
^
Refer to Table II for the appropriate
duct diameter for the effective duct
length.
Table II
Maximum effective
duct length allowable
Internal duct diam
-
eter required
20 m
40 m
100 m
100 mm
125 mm
150 mm
Installation - venting
37
Table I
Additional
duct length
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 or 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 inte
-
grated 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
* These can be obtained from the Miele Spare
Parts department or from builders’ merchants.