21
8.0 Flue Options
© 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
135°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
135°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 135° 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° bend
0.5 metre for each 135° bend
8.2
Twin & Vertical Flue Systems
1. Maximum permissible equivalent flue lengths are:-
(18)
(24)
(28)
Vertical Concentric
5m
4m
3m
Vertical Twin Pipe
10m
12m
12m
2. Any additional “in line” bends in the flue system must
be taken into consideration. Their equivalent lengths
are:-
Concentric Pipes:
135° bend
0.5 metres
93° bend
1.0 metres
Twin Flue Pipe
135° 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.
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