Pag.8
4. Concentric duct system
The concentric duct system consists of a inner duct, 100 mm in diameter, and a outer duct, 150 mm in diameter.
These ducts are fitted concentrically; discharge of combustion gas is through the inner duct and supply of com-
bustion air to the appliance is between the inner and outer ducts. The wide range of elements enables a flexible
connection between appliance and outlet section. Various connections are possible using the concentric duct sys-
tem:
Through the roof surface. Through the exterior wall.
The route for this system can be constructed in various ways, but there are a number of important conditions :
• Horizontal duct length for roof outlet must be no more than 5 metres, measured between the bends.
• Total maximum duct length permitted is 12 metres (sum of duct length + nominal lengths of the bends).
• 90-degree bends have a nominal length of 2 metres.
• 45-degree bends have a nominal length of 1 metre.
• Assembly direction is very important. Always ensure that the black sealing rings in the inner
pipe point upwards.
• The outlet can be made anywhere in the roof surface or exterior wall (inlet and discharge in identical
pressure areas), but must comply with the regulations currently in force.
The concentric duct system consists of the following components: ( see page 14 )
A. Concentric pipe. I. Locking band
B. Concentric 45° bend. J. Adjustable roof plate
C. Wall bracket. K. Flat roof flashing aluminium
D. L. Storm collar / rosette
E. Concentric 90° bend. M. Horizontal terminal excentric
F. Wall band adjustable. N. Lead slope roof flashing 20°- 45°
G. Adjustable length. O. Vertical terminal
H. Flat roof plate. P. Slope roof flashing 5°- 30°
4.1 Connection to concentric Duct system
Direct external wall duct (see diagram 3, page 15).
Decide on the position of the appliance and connect up the wall duct set. The wall duct set will have to be short-
ened if the appliance is being installed directly against the wall (cavity wall for example). Possible use of the ra-
diation plate supplied should be taken into consideration in all layouts.
Exterior wall duct without bends (see illustration 4, page 15)
Always place a length of X=1 metre vertically on the appliance, directly followed by a 90-degree bend with a
length of 0.5 metres on top and the standard length exterior wall duct set, Y=0.6 metres. If required, this can be
increased to a maximum of X= 4 metres vertical duct length.
Exterior wall duct with horizontal bend (see illustration 5, page 15).
Always place a length of X=1 metre vertically on the appliance and the course can be continued with one 90-
degree bend (nominal length per bend is 2 metres). A maximum horizontal deviation of Y=4 metres can then be
made. Ensure there is adequate slope and take the horizontal length of the bend itself into account.
From 1 metre till 4 metres baffle plate - O - should be used. ( see page 12 Ill. 1 )
Important: In installation situation described as illustration 4 and 5 no LPG appliance can be used!
Note:
In some situations the flue pipe should possible be placed close to the wall. Thus the 90° bend can not make the
shortest radius; to overcome this the hole in the wall for the 90° bend can be made lightly oval shaped.
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