Maximum Lengths; Slope; Flue & Air Maximum Length Example - Keston Qudos 28s User, Installation And Servicing Instructions

WD420/3/2007 Chapter 3 - Boiler Location
air pipe can be used (contact your Keston stockist for details). Keston Composite 75mm
pipe MUST be painted where exposed to UV light.
Both 50mm flue outlet terminal and 50mm air inlet terminal are supplied and are illustrated
in Figure 3.8.1. Both terminals are identical. If 75mm terminals are required these can be
obtained from your Keston Boilers stockist. Request part numbers C.17.2.26.00.0
(terminals) and C.17.2.00.60.0 (50 to 75 adapters).
3.8.2

Maximum Lengths

The maximum lengths of both air inlet pipe and flue outlet pipe, when no bends are used,
are as detailed below.
However, each bend used has an equivalent length that must be deducted from the
maximum straight length stated above. Knuckle bends must not be used.
o
A 92.5 sweep elbow is equivalent to 1.0m straight length. A 45
0.5m straight length.
Maximum Air Inlet Length
Maximum Flue Outlet Length:
Maximum Total Flue and Air Intake Length :
Example (assuming 50mm muPVC flue and air pipework)
Air inlet uses two one 92.5
(i.e. a+b in figure 3.8.2) = 39.0m - 1.0m - 1.0m = 37.0m
Flue outlet uses one 92.5
Hence, maximum length permissible (i.e.
c+d in figure 3.8.2 = 20.0m - 1.0 m = 19.0m
3.8.3

Slope

'Horizontal' flue outlet pipework MUST
slope at least 2 degrees (32 mm per metre
run) downwards towards the boiler.
Pipework can be vertical. Only swept
elbows can be used.
Air inlet pipework can be truly horizontal or
vertical, or sloping in a downward direction
towards the boiler but in this case rain, etc.,
must be prevented from entering the pipe.
There must be no troughs in any of the
pipework, whether it be air inlet or flue
outlet.
Due the low temperature of the flue gases
further condensate will form within the flue
system. Drain points, with suitable traps,
must therefore be incorporated within the flue
system at the base of vertical flue sections in
excess of 6m, for 50mm muPVC pipe flue
systems. These additional condensate drains
must be run to discharge as detailed in
section 3.11. Such drain points can be
formed using standard muPVC fittings. Refer
to the example in Figure 3.8.3.
Installation & Servicing Instructions
The Keston Qudos 28s & Qudos 28sP Boilers
:
o
sweep elbows. Hence, maximum length permissible
o
sweep elbow.
o
bend is equivalent to
50mm
39.0m
20.0m
40.0m
FLUE
d
c
KESTON Qudos 28s
Figure 3.8.2 : Flue & Air Maximum Length Example
Figure 2.8.3 :
Flue Condensate Drain
Point Example
To Boiler
Tee Fitting
75mm
117.0m
60m
120.0m
AIR
b
a
6 in min.
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