[Illustration: BUILDING THE CABIN FIREPLACE]
If the chapters in this book were arranged in the order of their
importance from the standpoint of cabin features, this one, dealing with
fireplaces and chimneys, would probably come first. No matter what other
ideas you may have about a vacation cabin you will undoubtedly insist on
a fireplace as a dominant feature. To most people a cabin without one
just isn’t a cabin at all.
When it comes to building it you can have the work done a lot easier
than you can do it yourself. On the other hand, you’ll probably do a lot
of arguing with the mason because, strange as it seems, there appear to
be comparatively few masons who can build a fireplace and a chimney that
will work to perfection. The instructions here have been collected from
people who do know how, and if you follow them, you should have a
successful fireplace.
In the preceding chapter you have read about the fireplace foundation.
By the time the rest of the house is pretty well along this should be in
good condition for the next step.
A fireplace consists of four essential parts: the fire box itself, the
throat, the smoke chamber, and the flue. The shape and relationship of
these are very important. One simple relation to remember is that the
area of the fireplace opening should not be more than 10 times the area
of the flue. Some people say 12 times, but 10 is a better average.
[Illustration: Fig. 6. Construction of fireplace.]
THROAT OPENING FULL WIDTH OF FIREPLACE
CHIMNEY FLUE
FLUE LINING
SMOKE CHAMBER
SMOKE SHELF
DAMPER
THROAT
8″
FIREPLACE
The over-all dimensions of the fireplace, including mantel, are matters
of proportion and taste, governed by the size and shape of the room. In
almost every case the width of the opening should exceed the height. The
top of the opening should be at least 30 inches from the floor but not
much more than 40 inches unless it is at least six feet wide—and not
many cabins can stand a fireplace as big as that. For a six-foot opening
plan for a depth of about 24 inches. No fireplace should have a depth of
less than 18 inches. Remember, however, that the deeper your fire box
the less efficient it will be for heating purposes. The hearth should
extend at least a foot on either side of the opening and have a minimum
depth of 20 inches.
You may have the opening flush with the hearth, or, as some builders
prefer, lay a course of stone several inches high across the lower edge
and curve the bottom of the fire chamber up to it. Or you may elevate
the entire bottom of the fireplace. It is smart to plan the hearth flush
with the floor so that trash may be swept into the fireplace without
using a dustpan.
Rough native stone, of course, is the most interesting material for a
cabin fireplace and chimney. Brick seems too refined for the woods. If
you want the finished job to look as massive in appearance as possible,
don’t use stones that are too small.
The walls of a stone fireplace and chimney should be at least one foot
thick. But as a concession to safety, the entire fire box—back, sides
and floor—should be lined with good quality firebrick. The space between
the stone shell and firebrick lining is filled with concrete. Since the
back and sides of the interior must reflect the heat into the room, the
back must be slanted forward as it rises, running up straight about
one-third of the height of the opening from the hearth floor and then
slanting toward the front at an angle of from 23 to 30 degrees. The
sides should slope inward, as they approach the back at, roughly, an
angle of 60 degrees.
Regardless of whether the top of the fireplace opening is flat or
arched, you will need a strong support at this point. The best is an
iron bar about one-half inch thick and two inches wide. Extend it across
the width of the opening and set it firmly in the stonework at each
side. Any blacksmith can make this bar for you, and the curve he puts in
it will determine the arch of the opening. A “T” bar, set with the tail
of the “T” upward, is even better, since it is stronger and requires
less iron.
Behind the bar build a wooden form extending back several inches and
sloped slightly upward. Then lay a course of stone on top of the iron
and fill in between the stone and the form with a rich mixture of
concrete reinforced with iron rods. This concrete should rise at such an
angle as to come flush with the edge of the damper. The reinforcing rods
should extend the full width of the arch and tie into the stone at the
sides.