Baxi 748 Installer's Manual page 10

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
not less than 120mm (See 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.
3.2.4 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.
3.3 The following flues are suitable:
225mm x 225mm conventional brick flue.
!
If a flue liner is used, it must be a minimum of 125mm diameter. 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 flue conforming to B.S 1289 or BS EN 1806.
!
A flue pipe with a minimum diameter of 127mm. See B.S 6461 Part 1 for suitable
!
materials. Metal flue pipes must comply with BS EN 1856 or BS 715.
3.3.1 The minimum effective height of the flue must be 3m.
3.3.2 The flue must be clear of any obstruction and its base must be clear of debris.
3.3.3 The flue must be completely sealed so that combustion products do not come into
contact with combustible materials outside the chimney.
©
Baxi Heating U.K. Limited 2006.
INSTALLER GUIDE
Figure 3. Pre-cast fireplace
Page 10