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• Where possible once the stove position has been
settled upon any significant gaps along the side and
back of the inset stove should be filled with a suitable
inert material such as rockwool. A vermiculite and
cement mix (6 parts vermiculite to 1 part cement)
can be used for filling large spaces – but under no
circumstances should it be packed against the stove
sides or pipework thus limiting the potential for the
stove to be accessed or easily removed at some later
point.
Flue Draught
The Precision Inset Boiler has been tested with a flue
draught pressure of 12pa and therefore to ensure
performance which is in line with the test results on
page 3 the ideal flue draught pressure should be
approximately 12Pa.
The Chimney, Flue and Flexible Liners
Other flued appliances must not share or be
connected to the same flue system or chimney as this
stove.
Generally speaking, the chimney or flue terminal
must be above the height of the apex of the building
and any other obstructions, such as trees, which are
within 3m (10’) of the flue terminal. Failure to do this
could affect the efficiency of the stove and may also
cause unwelcome down-draughts which would mean
potentially dangerous flue gases could be emitted into
room.
If you are using an existing chimney and it has been
checked for condition and suitability (see below), in
the interests of safety you must ensure that it is swept
before the stove is installed, even if it has never been
used or you intend to use a flexible liner. To find a
local registered sweep visit The National Association of
Chimney Sweeps at
www.chimneyworks.co.uk
or the
Guild of Master Chimney Sweeps at
www.guildofmasterchimneysweeps.co.uk
.
The recommended minimum height for the chimney /
flue system from the top of the stove to the top of the
chimney terminal is 4.5m (15’). If this is not possible
then a ‘spinner’ type cowl, to compensate for any po-
tential limited up-draught, should always be specified
and specialist advice sought on the correct type.
Under no circumstances should the stove’s 150mm
(6”) diameter flue be reduced in any part of the flue
system as this could cause a build-up of dangerous
carbon monoxide gas.
When your new inset boiler stove is installed with a
flexible flue liner it should be possible to sweep the
chimney through the stove by simply removing the
baffle plate inside the ‘roof’ of the stove. However, if
you do not use a liner the installer should, if possible,
provide an alternative means, such as a soot door
with adequate air-tight seal, in the chimney wall to be
able to clean the whole of the chimney / flue system.
Since stoves create flue gases at a much greater
temperature than those produced by an open fire or
gas appliance it does not necessarily follow that your
chimney will function adequately (or safely) when
your new stove is installed. The best way to ensure
that you have a fully functioning flue system is to fit
an approved flexible multi fuel flue liner. If you intend
to predominantly burn mineral fuels then 904L grade
liner will provide greater resistance to any acidic
condensates produced by burning certain mineral
fuels.
Precision strongly recommend fitting a chimney liner
for the following reasons:
• A flue liner is a major ‘quantifiable’ component in
a total and fully functioning flue system. As such it
will provide a consistent flue draught from the stove
through to the chimney terminal and when back-filled
with vermiculite will deliver much needed insulation
to keep flue gases as hot as possible (particularly
important for boiler stoves) which will help minimise
the amount of smoke produced. It will also improve
the stove’s operation with greater control over the
fuel burn rate and improve environmental and fuel
efficiency.
• Your existing chimney could leak smoke, fumes and
potentially dangerous ‘invisible’ carbon monoxide into
other parts of the building.
• Condensation or creosote ‘tar’, often associated
with burning wood, could eventually seep through the
walls, particularly if they are made of old or porous
brick and / or are jointed with lime mortar, eventually
causing unsightly stains on decorative coverings.
• Stoves work best with the correct draught. Pre-1965
chimneys which have been built for open fires have
larger (and irregular shaped) voids than those best
suited for a modern stove and thus could reduce the
effectiveness of the flue draught by making the flue
too cold and difficult to warm. This is a particular
problem if the chimney breast is on an outside wall
and / or is subject to a strong prevailing wind.
• The interior surfaces of older flues could be eroded
and also have rough surfaces which could cause
resistance to the smooth flow of gases and
consequently result in poor up-draught.
• Unfortunately many houses built since 1965 with
clay or concrete chimney liners suffer from these
being poorly installed, either through being fitted the
wrong way up or not receiving an appropriate
application of mortar to make a complete seal on
each joint. Even though not particularly old, this could
still potentially cause leaking smoke and fumes or
condensation stains
Your approved installer will be able to advise you on
the suitability of your chimney after undertaking a
thorough inspection and smoke test. Any solid fuel
flexible liner which is specified should be double
skinned stainless steel, either 904L or 316Ti grade and
be CE marked and / or Hetas Approved.
