y and other flues. Considerable skill is required in [Sidenote:
Chimneys and flues.] gathering-over properly above the fireplace so as to
conduct the smoke into the smaller flue, which itself requires to be built
with precision, so that its capacity may not vary in different parts. Bends
must be made in gradual curves so as to offer the least possible resistance
to the up-draught, and at least one bend of not less than 60 deg. should be
formed in each flue to intercept down-draughts. Every fireplace must have a
separate flue. The collection of a number of flues into a "stack" is
economical, and tends to increase the efficiency of the flues, the heat
from one flue assisting the up-draught in those adjoining it. It is also
desirable from an aesthetic point of view, for a number of single flue
chimneys sticking up from various parts of the roof would appear most
unsightly. The architects of the Elizabethan and later periods were masters
of this difficult art of treating a stack or stacks as an architectural
feature. The shaft should be carried well above the roof, higher, if
possible, than adjacent buildings, which are apt to cause down-draught and
make the chimney smoke. When this is found impossible, one of the many
forms of patent chimney-pots or revolving cowls must be adopted. Each flue
must be separated by smoke-proof "withes" or divisions, usually half a
brick in thickness; connexion between them causes smoky chimneys. The size
of the flue for an ordinary grate is 14x9 in.; for a kitchen stove 14x14
in. The outer wall of a chimney stack may with advantage be made 9 in.
thick. Fireclay tubes, rectangular or circular in transverse section, are
largely used in place of the pargetting; although more expensive than the
latter they have the advantage in point of cleanliness and durability.
Fireplaces generally require more depth than can be provided in the
thickness of the wall, and therefore necessitate a projection to contain
the fireplace and flues, called the "chimney breast." Sometimes, especially
when the wall is an external one, the projection may be made on the back,
thus allowing a flush wall in the room and giving more space and a more
conveniently-shaped room. The projection on the outside face of the wall
may be treated as an ornamental feature. The fireplace opening is covered
by a brick relieving arch, which is fortified by wrought-iron bar from 1/2 to
3/4 in. thick and 2 to 3 in. wide. It is usually bent to a "