INSTALLER’S GUIDE
Page 8
A precast concrete or clay flue
block system conforming to
BS1289 with dimensions as in
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.
2.2.3
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.
2.4
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
Figure 3. Precast or clay flue block system