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.
4.2.4
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.
4.3
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 Part 2.
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
BS EN 1856 Part 1. 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 concrete or clay flue system conforming to BS1289
or BS EN 1858. This system is only suitable if the conditions stated in section 4.2.3
are met.
4.4
The flue must conform to BS 5440: Part 1 in design and installation.
The flue, measured from the bottom of the fireplace opening to the bottom of the
terminal, shall be not less than 3m in actual vertical height. When calculated in
©
Baxi Heating U.K. Limited 2008.
Page 11
INSTALLER GUIDE
Figure 3. Precast or clay flue block system
