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3.10.3 Precast concrete or clay
flue block system and hearth.
The appliance can be installed to a
precast concrete or clay flue block
system conforming to BS EN 1858
with dimensions as in figure 8.
BS 1289 part 1 recommends 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.
3.11 Flues.
1. 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 BS4543 Part 2.
-
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. 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 1858. This system is only suitable if the conditions stated in section 3.10.3
are met.
© GDC Group Ltd. 2012
INSTALLER GUIDE
Figure 8. Precast or clay flue block system
Page 16
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