2.8.3
Boiler Output vs Flue Length
Due to the resistance presented by extended flue length a slight reduction in
maximum boiler output will occur where flue lengths in excess of 8m (50mm
muPVC), or 24m (Friaphon DN70) are used. In such cases the boiler output will
be reduced by 1% per additional 1m (50mm muPVC) and 1% per additional 3m
(Friaphon DN70).
2.8.4
Slope
'Horizontal' flue outlet pipework
MUST slope at least 3.5 degrees
(61
mm
per
metre
run)
downwards towards the boiler
where 50mm muPVC pipe is
used. In the event 75mm Friatec
pipe wise used a slope at least 2
degrees (35mm per metre run)
can be used. 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 3m, for
50mm muPVC pipe flue systems. These additional condensate drains must be
run to discharge as detailed in section 2.11. Such drain points can be formed
using standard plastic fittings. Refer to the example in Figure 2.8.3.
2.8.5
Terminations
Air inlet terminals must be facing horizontally or downwards to prevent entry of
rain into the terminal 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 invalidates the
heat exchanger warranty.
The flue outlet terminal is designed to face outwards but can, if desired, be
adapted to face in any direction BUT must not be directed in the region of the air
inlet.
The two terminals are subject to the requirements of BS 5440 Pt 1 for clearances
from features of the building although some can be decreased to the values
indicated.
The Keston C45, C40P and C55(P), as with any condensing boiler, will
generate a condensate “plume” from the flue terminal in all weather
conditions. Consideration must therefore be given to the effect of this
“plume” when selecting a location for the flue terminal.
It is advisable for horizontal flue terminals to place a 45
o
elbow at the end of the
flue to direct the condensate plume up and away from the property.
WD536
Chapter 2 - Boiler Location
The Keston C45, C40P, C55 & C55P
Installation & Servicing Instructions
Page : 16
6 in min.
Figure 2.8.3 :
Flue Condensate Drain
Point Example
Tee Fitting
To Boiler
To
T
er
m
in
al