s
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.
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 B.S 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.
3.3.4
The flue must serve only one fireplace.
Page 8
INSTALLER GUIDE
Figure 3. Pre-cast fireplace
