4.2.3
A precast concrete or clay flue
block system conforming to BS EN
1806 or BS 1289 with dimensions as
in figure 3. The current versions of
BS1289 and BS EN 1806 recommend
that there should be an air space or
insulation between the flue blocks and
the plaster because heat transfer may
cause cracking on directly plastered
flues. However, generally this
appliance is suitable for installations
under all circumstances unless there is
a history of cracking problems.
Remember that faults such as
cracking may be caused by poorly
built and restrictive flues, e.g. mortar
extrusions, too many bends, flue
heights below three metres, restrictive
terminations etc (See figure3).
4.2.4
If the fireplace opening is
greater than the acceptable
dimensions given in this guide, do not
use the back of a fire surround or
marble to reduce the opening. This
may cause cracking of the surround back or marble.
4.3
Suitable flues and minimum flue sizes are as follows: -
It should be noted that, as with many appliances, sharp bends or horizontal runs in
metal flues at the top of the system can be a cause of problems in these types of
installation.
!
225mm x 225mm conventional brick flue.
!
175mm diameter lined brick or stone flue.
!
200mm diameter factory made insulated flue manufactured to the current edition of
BS EN 1859 or BS 4543.
!
175mm diameter flue pipe. See BS6461 Part 1 for suitable materials.
!
Single wall, twin wall or flexible flue liner with a minimum diameter of 125mm.
The materials to be used are stainless steel or aluminium as specified in BS EN 1856
Part 1 or BS 715. The liner must be sealed to the surrounding area above the fireplace
opening and to the top of the chimney. An approved terminal must be fitted.
!
A properly constructed precast concrete or clay flue system conforming to BS1289
or BS EN 1806. This system is only suitable if the conditions stated in section 4.2.3 are
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INSTALLER GUIDE
Figure 3. Precast or clay flue block system
dimensions
