8.0 Flue Options
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© Baxi Heating UK Ltd 2014
Y
8.2
Twin & Vertical Flue Systems
Concentric
The maximum equivalent lengths are 4m
(vertical). Their
lengths exclude the standard elbow and terminal assembly
(vertical).
Twin Flue
The total maximum equivalent flue length is 150m.
NOTE:
Each 1m of flue duct should be calculated as 2m.
Any additional “in line” bends in the flue system must be
taken into consideration. Their equivalent lengths are:
Concentric Pipes:
135° bend
0.5 m
93° bend
1.0 m
Twin Flue Pipe:
135° bend (air duct)
1.3 m
135° bend (flue duct)
2.6 m
90° bend (air duct)
4.8 m
90° bend (flue duct)
9.6 m
IMPORTANT:
All flue systems must be securely
supported at least once every metre. Suitable pipe
supports are available as accessories.
The total equivalent length
for this example is
17.2 + 34.4 = 51.6 metres.
1m extension
135°bend
91.5°bend
1m
1.3m
4.8m
5
2
2
5.0m
2.6m
9.6m
AIR DUCT
N
o
of
fittings/pipes
Sub total
Equivalent
Length Value
Equivalent Length Air Duct =
17.2m
1m extension
135°bend
91.5°bend
2m
2.6m
9.6m
5
2
2
10.0m
5.2m
19.2m
FLUE DUCT
N
o
of
fittings/pipes
Sub total
Equivalent
Length Value
Equivalent Length Flue Duct =
34.4m
Y
X
C
Roof
Terminal
A
B
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
X
Y
X
Vertical Flue
System Examples
Vertical Flue System
Examples (Twin Pipe)
