To Calculate The Total Duct Length - Miele PT 5136 OS Operating And Installation Instructions

Installation - extraction ducting
To calculate the total duct
length
Friction against the inner walls of the
vent ducting will slow down the
expelled air as it passes through the
ducting. 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 duct length factors are
calculated by comparing the friction
created by, for example, an elbow to
that created by 1 metre of straight
plastic piping (see Table 1).
The additional duct length factor for
each item needs to be added together
to ascertain the total duct length which
will be needed for the venting system.
The total duct length is a means of
calculating the friction created by the
venting system as a whole.
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 (see
Table II).

To calculate the total duct length

1. First measure the distance requiring
straight ducting. Multiply this amount
by the corresponding additional
length factor in Table I.
2. Establish the number of angles,
bends etc., and add their additional
length factors together with the help
of Table I.
3. Add all the additional length factors
to give the total duct length.
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4. Refer to Table II for the appropriate
duct diameter required.
Table I
Component
Flexible ducting*
–
1 m laid straight
–
45° angle
(Bend radius = 0.25 m)
–
90° angle
(Bend radius = 0.25 m)
Flexible aluminium
ducting*/plastic piping
–
1 m laid straight, or 1 m
straight pipe
–
45° angle
(Bend radius = 0.25 m)
–
90° angle
(Bend radius = 0.25 m)
Wall vent kit* or window vent
kit*
–
with louvred grill
–
with non-return flap (hinged
flap)
Non-return flap* integrated into
the vent ducting
Flat ducting (for washer-dryer
stack)*
Venting connection to the
left/right
* optional accessory
Table II
Maximum total
duct length allowable
20 m
40 m
80 m
Additional
duct
length
factor
1.8 m
1.5 m
2.5 m
1.0 m
0.6 m
0.8 m
3.8 m
1.5 m
14.3 m
11.0 m
1.0 m
Internal duct
diameter required
100 mm
125 mm
150 mm