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 6. 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.
3.11 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.
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 BS715. 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.
Page 15
©
Baxi Heating U.K. Limited 2010.
INSTALLER GUIDE
Figure 6. Precast or clay flue block system
