Precast Concrete Or Clay Flue Block System And Hearth - Valor Fires 953 Installer And Owner Manual

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 BS1289 or BS EN 1858 with dimensions as in figure 6.
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.
The appliance is suitable for installations conforming to older versions of BS1289 as
well as the current edition. The flue blocks must have a minimum width not less than
63mm and a cross-sectional area not less than 13,000mm 2 . Older editions of BS1289
required a cross-sectional area of 13,000mm 2 . The current revision of the standard
requires 16,500mm 2 . This appliance is suitable in both cases. The total depth of the
opening measured from the finished front of the fireplace (Including plaster, surround
etc.) must be as below:
If the width at the rear of the
precast flue starter blocks is 300mm
or greater the depth of the opening
is to be not less than 138mm. Under
these conditions the eyebolts will
need to be located as close to the
sides of the starter blocks as
possible.
If the width at the rear of the
precast flue starter blocks is less
than 300mm then an additional
16mm of depth will be required to
accommodate the eye bolts.
Therefore if the starter blocks are
less than 300mm wide the minimum
depth of the opening will be not less
than 154mm.
©
Baxi Heating U.K. Limited 2010.
INSTALLER GUIDE
Figure 6. Pre-cast Fireplace
Page 16