5.6
Pipe lengths
As the resistance of the flue discharge and air supply pipes increases,
the capacity of the appliance will decrease. The maximum allowed
power decrease is 5%.
The resistance of the air supply and the flue discharge depends on the
length, the diameter and all components of the pipe system. The total
allowed pipe lengths of the air supply and the flue discharge are given
below:-
Note for twin pipes
The total pipe length is:-
The length of all straight pipe lengths and the
lengths of the equivalent pipe lengths of bends.
The maximum length of the air supply and flue
discharge 80mm pipes added together is 60 m.
Note for concentric pipes
The total pipe length is:-
The length of all straight pipe lengths and the
lengths of the equivalent pipe lengths of bends.
The maximum length of the 80/125mm concentric
pipe is 24 m for horizontal pipe and 27 m for vertical
pipe.
5.6.1
Equivalent lengths
Bend at 90°
R/D=1
2 m
Bend at 45°
R/D=1
1 m
Elbow at 90°
R/D=0.5
4 m
Elbow at 45°
R/D=0.5
2 m
Note – The type supplied by Atmos are Elbows.
For smaller twin pipe diameters, the maximum pipe length is reduced as
follows:-
70mm dia:
0.59 x max. pipe length for 80mm dia.
60mm dia:
0.32 x max. pipe length for 80mm dia.
50mm dia:
0.15 x max. pipe length for 80mm dia.
Note that Atmos only supply 80mm twin pipes
5.6.2
Example of 80mm twin pipe calculation
See diagram.
Pipe
Pipe lengths
Total pipe lengths
Flue discharge L1 + L2 + L3 + 2 x 2 m 13 m
Air supply
L4 + L5 + L6 + 2 x 2 m 12 m
Total length
25m
5.6.3
Example of 80/125mm concentric pipe calculation
With 3 elbows at 90°, the max straight length of concentric pipe that can
be used is 24m – 3x4m = 12m.
26