While the chimney may be made one of the most charming and
effective elements of the house design, its structural and
practical necessities are its most striking features.
The proper construction, size, and height of chimneys are of the
utmost importance both for the successful working of the heating
system and for the prevention of fires. The chimney may, though
it need not be, a point of danger to the safety of the home. A
little intelligent care in its construction will prove to be the
best insurance. As a first precaution, all wood framing of floor
and roof must be kept at least 2 inches away from the chimney and
no other woodwork of any kind be projected into the brickwork
surrounding the flues.
[Illustration: Fig. 17. Chimney Height]
Chimneys should be tightly built of solid brick, have no openings
except those required for the connection of the heating apparatus,
and should always extend at least one foot above the highest point
of the roof. In some cases, depending on local surroundings, it may
be desirable to carry them somewhat higher. Those terminating below
the level of the roof usually have poor draft because the wind,
sweeping across or against the roof, may form eddies that drive
down the chimney or check the natural rise of the smoke (Fig. 17).
[Sidenote: Flue Lining]
The flues of chimneys should not start from the bottom of the
foundation but only about a foot below the first smoke pipe
openings, and should be lined with terra cotta flue lining their
entire height. Care should be taken in setting flue linings to be
sure that the joints are well cemented and, at the same time, that
all spaces between the lining and brickwork are tightly filled with
mortar. Any openings in the joints of the tile lining, or even of
the brickwork, not only check the draft but are a fire menace.
Cement plaster should not be substituted for the flue lining as
it is likely to crack and fall off, thus leaving the flue in a
dangerous condition. However, where flue linings are not available,
a strong smooth cement plaster may be used, in which case the
chimney wall should be at least 8 inches thick.
Modern heating plants necessitate accurate construction of
chimneys, and most manufacturers of heating apparatus nowadays
recommend the area and height of the flue necessary for their
installations. The following table will prove useful in considering
the question of heating plant or fireplace, by showing the
dimensions of flue linings to be ordered when the required area is
ascertained.