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RATIO PROBLEM |
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The
FIREPLACE OPENING is too large for size of FLUE, i.e. the volume and speed of
the smoke passing up the flue is insufficient to clear the large volume of
fumes building up in the oversize fireplace opening below.
Flues above 6m tall should generally be not less than 1/7th to 1/8th of the
area of the fireplace opening, e.g. a 225 mm (9") diameter flue will
support a fireplace opening up to about 550 x 550 mm (22" x 22")
(see Building Regulations J 2.2.) For bungalows, the ratio should be reduced
to 1/6th. As
it is generally impractical to consider rebuilding the flue to a larger size,
the fireplace opening must be reduced. There are a number of ways this may be
done, depending on the size of the original fire opening and the purpose for
which the fire is intended. For larger fireplaces and inglenooks,
the whole flue should be closed off with a horizontal register plate just
above beam or lintel height. A freestanding fire, bricked-in convector open fire, closed stove, or canopy
can then be fitted with a flue projecting through the register plate. An
access trap must be provided
for cleaning above the register plate.
For smaller fire openings (up to say 900 mm (3') square, a smoke hood,
canopy or tempered plate glass strip, can be fitted across the full width of
the fire opening, effectively
lowering the height of the lintel. It is best to experiment first, using a
strip of sheet metal, fireproof board or even hardboard pinned or wedged in
position. (Do not leave the fire unattended if hardboard is used.) This can
be lowered until the fire no longer smokes before making a permanent job. Try
the experiment for a couple of weeks before finally accepting success. A
raised plinth can also be built to reduce the opening
size. This can be temporarily built from old bricks built loose and jointed
with dry sand. (See diagram 1.) Installing a convector fire box is also a
good solution in this situation. |
