Flues - Valor 940 Installer And Owner Manual

3.10.2 Metal flue box and hearth.
The appliance can be installed to
a fireplace incorporating a metal
flue box complying with the
constructional requirements of
the current edition of BS 715 and
with a flue conforming to BS EN
1856 part 1. The dimensions of
the flue box must conform to
those shown in figure 7.
The top of the metal flue box
must be covered with a 100mm
layer of mineral wool or
equivalent insulation (See figure
7).
Important Note: Where the flue
box has a base sheet that is
single wall (i.e. a single metal
sheet) the flue box must be
mounted on a non-combustible
hearth. The hearth material must
be at least 12mm thick.
3.10.3 Precast concrete or clay flue block system and hearth.
To a precast concrete or clay flue block system conforming to BS1289 with
dimensions as in figure 8. The current versions of BS1289 and BS EN 1858
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.

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.
125mm or 175mm diameter lined brick or stone flue.
200mm diameter factory made insulated flue manufactured to BS4543.
©
GDC Group Ltd. 2011
INSTALLER GUIDE
Figure 7. Metal Flue box dimensions
Page 16