system and a pump selected that is capable of meeting the flow rate required at
the total pressure loss generated by the boiler and the rest of the system. The
selected pump must comply with BS 1394. It is important to note that the
minimum flow rate must be maintained whenever the boiler is firing. Systems
using zone valves must be specifically designed to only fire the boiler when the
pump is running and the minimum flow rate can be achieved.
2.8
FLUE SYSTEM
2.8.1
Design
Individual air supply and flue outlet pipes are used. The material used for flue
outlet &/or air inlet must be
muPVC
to BS 5255 an of an internal diameter of 51
mm.
Both flue outlet terminal and air inlet terminal are supplied and are illustrated in
Figure 2.8.1 above.
2.8.2
Maximum Lengths
The maximum lengths of both air inlet pipe and flue outlet pipe, when no bends
are used, are as detailed below.
Maximum Air Inlet Length
:
15.0 m
Maximum Flue Outlet Length
:
15.0 m
However, each bend used has an equivalent length that must be deducted from
the maximum straight length stated above. Knuckle bends must not be used.
A 92.5
o
sweep elbow is equivalent to 1.0m straight length.
Example:
Air inlet uses two one 92.5
o
sweep elbows. Hence, maximum length permissible
(ie a+b in figure 2.8.2) = 15.0m - 1.0m - 1.0m = 13.0m
Flue outlet uses one 92.5
o
sweep elbow. Hence, maximum length permissible (ie
c+d in figure 2.8.2) = 15.0m - 1.0 m = 14.0m
WD51/2/1997 Chapter 2 - Boiler Connections The Keston 170 Condensing Boiler
Installation & Servicing Instructions
Page : 11
Flue Outlet Terminal
Air Intake Terminal
Figure 2.8.1 : Terminals
O56
80
40
87
211
O56
O83
