Calculating the total ductlength :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 total duct length
required.
A larger internal duct diameter also
helps reduce friction. If the total duct
length is more than 20 m the duct
diameter should be increased (Table
II).
1. To calculate the total 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 total duct
length.
2. Internal duct diameter
^Refer to Table II for the appropriate
duct diameter required.
Table I
Additional
ductlength
factor
Flexibleducting*
–1m laid straight
–45°angle
(Bendradius = 0.25 m)
–90°angle
(Bendradius = 0.25 m)
1.8m
1.5m
2.5m
Flexiblealuminium vent hose* / plastic
piping
–1m laid straight / or 1 m
straightpipe
–45°angle / elbow
(Bendradius = 0.25 m)
–90°angle / elbow
(Bendradius = 0.25 m)
1.0m
0.6m
0.8m
Wallvent kit* or window vent kit*
–withlouvred grille
–withnon-return flap (hinged
flap)
3.8m
1.5m
Non-returnflap* to be
integratedinto the vent
ducting
14.3m
Flatducting (for washer dryer
stack)*
11.0m
Ventingconnection to the
left/right
1.0m
*optionalaccessory from Miele
Table II
Maximumtotal
ductlength allowable
Internalduct
diameterrequired
20m
40m
100m
100mm
125mm
150mm
Installation - venting
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