4
17
Fig. 8
Principal Dimensions (mm)
change should be as gentle as possible. If there is any doubt about the flue configuration, the equivalent flue height
should be determined (see 5.1.10).
5.1.9
If the appliance to be fitted is a replacement, the old appliance should be checked for signs of spillage prior to
commencement of the installation and appropriate action taken, (i.e. check flue system and renew as necessary).
5.1.10 It is recommended that at least 600mm of vertical flue should be provided from the top of the draught diverter (for
new installations this shall be incorporated into the flue design). However, when carrying out replacement
installations, an existing flue system may be encountered, where the vertical flue above the appliance to the first
bend is less than 600mm. In the first instance, the installer must judge whether this distance can be achieved
practicably by some means. Where this is not practicable, the existing flue system may be used, providing there is no
evidence of spillage from the old appliance (see 5.1.9 above). Every effort must be made, however, to ensure that the
existing flue complies in every other way to BS 5440 Part 1, including the visual inspection, flue flow and spillage test
described in 4.3.2 of the above standard. Flue configurations may be assessed in terms of equivalent vertical height -
details are given in 5.1.11. For air heaters, the minimum equivalent vertical height is 1 metre. The installer must make a
judgement based on his knowledge and experience and the examination and testing described above as to whether
an existing flue system can be used.
Note:
Ventilation of the compartment, room or internal space in which the appliance is to be installed must be checked for
compliance with the requirements of BS 5440 Part 2 ( Ref. Section 3 of these instructions) and upgraded as necessary.
Component
Internal Size (mm)
Resistance
Components
Internal Size (mm)
Resistance
Flue Blocks
197 x 67
0.85 per metre
45
o
bend
100mm pipe
0.61 per fitting
231 x 65
0.65 run
125mm pipe
0.25 per fitting
317 x 63
0.35
150mm pipe
0.12 per fitting
140 x 102
0.60
197 x 67
0.30 per fitting
200 x 75
0.60
231 x 65
0.22 per fitting
183 x 90
0.45
317 x 63
0.13 per fitting
Pipe
100
0.78
Raking Block
Any
0.30 per block
125
0.25
150
0.12
Adaptor Block
Any
0.50 per block
Chimney
213 x 213
0.02
Terminal
100mm ridge
2.5
125mm ridge
1.0
90
o
Bend
100mm pipe
1.22 per fitting
150mm ridge
0.48
125mm pipe
0.50 per fitting
100mm GCI
0.6
150mm pipe
0.24 per fitting
125mm GCI
0.25
150mm GCI
0.12
Appliance
Inlet Resistance (K
i
)
Flue
Outlet resistance (K
o
)
100mm Dia Spigot
2.5
100mm
2.5
125mm Dia Spigot
1.0
125mm
1.0
150mm Dia Spigot
0.48
150mm
0.48
Table 3
Inlet and outlet resistances
Table 2
Resistance factors for use in calculating equivalent heights
