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8.0 Flue Options
19
© Baxi Heating UK Ltd 2007
Vertical
Flues
(Twin Pipe)
Y
X
Vertical
Flues
Y
X
The total equivalent length for this example is
= 6.5 metres.
1m extension
45°bend
91.5°bend
1m
0.25m
0.5m
5
2
2
5.0m
0.5m
1.0m
AIR DUCT
N
o
of
fittings/pipes
Sub total
Equivalent
Length Value
Equivalent Length Air Duct = 6.5m
1m extension
45°bend
91.5°bend
1m
0.25m
0.5m
5
2
2
5.0m
0.5m
1.0m
FLUE DUCT
N
o
of
fittings/pipes
Sub total
Equivalent
Length Value
Equivalent Length Flue Duct = 6.5m
Y
X
C
Roof
Terminal
A
B
660mm
This bend is equivalent to
1 metre
Total Equivalent Length =
A+B+C+1x90°Bend
All vertical and angled runs must be included,
measured from the boiler adaptor (point X) to the
joint with the flue terminal (point Y). One 91.5°
bend or two 45° bends can be included without
reduction of the flue length.
If further elbows are required the flue length must
be reduced by the following amounts:-
1 metre for each 91.5° elbow
0.5 metre for each 45° elbow
8.2 Twin & Vertical Flue Systems
1. Maximum permissible equivalent flue lengths are:-
Vertical Concentric 3m
Vertical Twin Pipe 12m*
* Both the air and flue duct can be up to 12 metres
long each.
4. Any additional “in line” bends in the flue system must
be taken into consideration. Their equivalent lengths
are:-
Concentric Pipes:
45° bend 0.5 metres
93° bend 1.0 metres
Twin Flue Pipe
45° bend 0.25 metres
91.5° bend 0.50 metres
The elbow supplied with the standard horizontal flue is
not included in any equivalent length calculations
NOTE: Flue length is measured from point X to Y
as shown.