9.0 Plume Displacement
24 © Baxi Heating UK Ltd 2009
Concentric 60/100 Flue
60Ø Exhaust
XY
Fig. 17
2
0
1
60 Ø Exhaust (metres) X
Concentric 60/100 Flue (metres) Y
0
2
1
3
3
24
Fig. 18
2
0
1
60 Ø Exhaust (metres) X
Concentric 60/100 Flue (metres) Y
0
2
1
3
3
24
2
0
1
60 Ø Exhaust (metres) X
Concentric 60/100 Flue (metres) Y
0
2
1
3
3
24
Flue Length - Worked Example
Potterton Performa 24 Eco HE
In Fig. 18 opposite an additional 93° bend has been included
in the 60Ø exhaust. with 2 x 1metre extensions which have
been cut to 0.25metres and fitted. The waste is discarded.
To calculate total length:-
2 x 0.25 metre Lengths = 0.5 metres
1 x 93° Elbow = 1 metre
Total 60Ø Exhaust = 1.5 metres
After consulting the table in Example 3 it can be determined
that the concentric flue could be up to approximately 0.5
metres long.
Concentric Flue
Support
Bracket
93° Elbow
Extension
Additional Accessories
A - 93° Elbow 5117381
B - 45° Elbow (Pair) 5117382
C - 1 metre 60Ø Extension 5117380

9.2 Determining Permissible Lengths

In the graph the solid line diagonal represents the
relationship between the concentric flue assembly (and any
extensions) and the 60Ø exhaust (and any extensions or
additional bends).
Example 1 - Not Permissible
If, for instance, a concentric length of 2 metres was required
and the 60Ø exhaust needed to be 1.5 metres the graph
shows that this combination would NOT be permissible as
the intersection point would be above the solid diagonal line.
Example 2 - Flue Lengths OK
Where both lengths have been determined they can be
applied to the graph to check that the installation is
permissible. For example, if it was known that 1 metre of
concentric flue and 1.5 metres of 60Ø exhaust were
required, the values could be applied to the graph as shown
in Example 2.. As the point of intersection of the dotted lines
is below the solid diagonal line, the combination of lengths is
shown to be acceptable.
Example 3 - Flue Lengths OK
In the example shown, assume that the concentric part of
the flue needs to be 1 metres long. Find the position of ‘1’ on
the horizontal axis of the graph and then project upwards to
the solid diagonal line. This is represented by the vertical
thick dotted line. Where this dotted line intersects with the
solid diagonal line on the graph, project across to the vertical
axis. As can be seen this corresponds with 2 metres.
Therefore, the total equivalent length of the 60Ø exhaust
can be up to 2 metres. Any bend equivalencies must be
accounted for i.e. 93° bends are equal to 1 metre, each 45°
bend to 0.5 metres.
Example 1
Flue Lengths - Not Permissible
Example 2
Flue Lengths - OK
Example 3
Flue Lengths - OK