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WD53/0/1999
Chapter 2 - Boiler Connections
Example:
Air inlet uses two
one 92.5
elbows. Hence,
maximum length
permissible (ie a+b
in figure 2.8.2) =
20.0m - 1.0m - 1.0m
= 18.0m
Flue outlet uses one
o
92.5
sweep elbow.
Hence, maximum
length permissible
(ie c+d in figure 7 =
40.0m - 1.0 m - total
air inlet length =
39.0m - total air inlet
length.
2.7.3
Slope
'Horizontal' flue outlet pipework
MUST slope at least 2.5
degrees (45 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 4m. These
additional condensate drains must be run to discharge as detailed in section 2.10.
Such drain points can be formed using standard Keston Composite flue fittings.
Refer to the example in Figure 2.7.3.
2.7.4
Terminations
Air inlet terminals must be facing downwards and positioned to ensure only fresh
air is drawn into the boiler. The air terminal must be located outside of the
building.
Drawing of combustion air directly from a ventilated boiler room will invalidate the
heat exchanger warranty.
The air inlet terminal must face downwards to prevent entry of rain into the air
intake pipework.
Installation & Servicing Instructions
o
sweep
Figure 2.7.2 : Flue & Air Maximum Length Example
The Keston 260 & 340 Condensing Boilers
FLUE
d
c
Keston
Figure 2.7.3:
Flue Condensate Drain
Point Example
To Boiler
Tee Fitting
AIR
b
a
6 in min.
Page : 10
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