The Franklin stove (fig. 19) is a type of modified fireplace.
The modified fireplaces of today are of several types, as shown in
figures 20 and 21.
Both the last two types of modified fireplaces are manufactured as units
of heavy metal, designed to be set into place and concealed by the usual
brickwork, or other construction, so that no practical change in mantel
design is required by their use. The modifications are built-in standard
parts of the fireplace--only the grilles show (fig. 22).
[Illustration: Figure 20.--In this modified fireplace air enters the
inlet, _a_, from outside and is heated as it rises by natural circulation
through the back chamber, _c_, and the tubes, _t_, being discharged into
the room from the register, _b_. Air for supporting combustion is drawn
into the fire at _d_ and passes between the tubes up the flue A damper is
also provided to close the air inlet.]
One advantage claimed for modified fireplace units is that the correctly
designed and proportioned firebox, manufactured with throat, damper,
smoke shelf, and chamber, provides a form for the masonry, thus reducing
the risk of failure and assuring a smokeless fireplace! However, there is
no excuse for using incorrect proportions; and the desirability of using
a foolproof form, as provided by the modified unit, merely to obtain good
proportions should be considered from the standpoint of cost. Even though
the unit is well designed, it will not operate properly if the chimney is
inadequate; therefore the rules for correct chimney construction must be
adhered to with the modified unit as well as with the ordinary fireplace.
Manufacturers claim labor and materials saved tend to offset the purchase
price of the unit; also that the saving in fuel justifies any net
increase in first cost. A minimum life of 20 years is claimed for the
type and thickness of metal commonly used today in these units.
Field tests made by this Bureau have proved that, when properly
installed, the better designs of modified-fireplace units circulate heat
into the cold corners of rooms and will deliver heated air through ducts
to adjoining or upper rooms. For example, heat could be diverted to a
bathroom from a living-room fireplace.
[Illustration: Figure 21.--In this fireplace the air is not drawn in
directly from outdoors but through the inlet, _a_, from the room that is
being heated. The air is heated by contact with the metal sides and back
of the fireplace, rises by natural circulation, and is discharged back
into the room from the outlet, _b_, or to another room on the same floor
or in the second story. The inlets and outlets are connected to registers
which may be located at the front of the fireplace, as shown in figure
22. The registers may be located on the ends of the fireplace or on the
wall of an adjacent room.]
The quantity and temperature of the heated air discharged from the
grilles in figures 20 and 21 were measured to determine the merits of
the convection features. These measurements showed that very appreciable
amounts of convected heat are produced by the modified unit when
properly installed and operated. Discharge-air temperatures in excess
of 200° F. were attained from some of the units tested. The heated air
delivered from the discharge grilles of some of the medium-sized units
represented a heating effect equivalent to that from nearly 40 square
feet of cast-iron radiation of the ordinary hot-water heating system, or
sufficient to heat a 15- by 18-foot room built with average tightness to
70° F. when the outside temperature is 40° F. Additional convected heat
can be produced with some models by the use of forced-circulation fans.
[Illustration: Figure 22.--Except for the registers and metallic sides
and back, the appearance of modified fireplaces is like that of ordinary
ones. An interesting effect is secured by the mirror--the reflection of
the opposite wall appears like a recess over the mantel.]
However, the nature of operation, with the unavoidably large quantity of
heated air passing up the stack, makes the inherent over-all efficiency
of any fireplace relatively low. Therefore, claims for an increased
efficiency of modified fireplaces should be understood merely as
constituting an improvement over the ordinary fireplace and not over
stoves or central heating plants.
When a fireplace is being selected the kind of fuel to be burned should
be considered; also, the design should harmonize with the room in
proportion and detail (figs. 23 and 24).
[Illustration: Figure 23.--A well-designed commercial mantel that suits
the room. Since it is painted the same color as the walls, it does not
focus attention, as the handsomely carved formal mantel or mahogany shown
in figure 37 is intended to do.]
In colonial days, when cordwood was plentiful, fireplaces 7 feet wide and
5 feet high were common, especially when used in kitchens for cooking
(fig. 25). They required large amounts of fuel and too frequently were
smoky.
Where cordwood (4 feet long) is cut in half, a 30-inch width is desirable
for a fireplace; but, where coal is burned, the opening can be narrower
(fig. 26). Thirty inches is a practical height for the convenient tending
of a fire where the width is less than 6 feet; openings about 30 inches
wide (fig. 27) are generally made with square corners. The higher the
opening, the greater the chance of a smoky fireplace.
[Illustration: Figure 24.--Another good design is this revival of early
New England architecture, which is frequently used for remodeling public
dining rooms. The random-width pine planks were selected especially for
variety in the pattern of the knots. Note the use of otherwise wasted
space for bookshelves and closet.]
[Illustration: Figure 25.--_A_, A fireplace at Mount Vernon, Washington's
home, typical of those used before cooking stoves were introduced.
This type of fireplace, if not too large, is often retained (_B_) when
a kitchen is remodeled into a living room. Note the Dutch oven at the
right, formerly used for baking.]
[Illustration: Figure 26.--Fireplaces originally intended for wood were
frequently bricked up, and small cast-iron units of this type were built
in, since the large openings required for wood were wasteful when coal
was used. This was a very popular type of grate for hotel and private
bedrooms about 1860 and can still be seen in old houses in coal regions.
Note the plain and neat mantel of wide plank.]
In general, the wider the opening the greater should be the depth. A
shallow opening throws out relatively more heat than a deep one of the
same width but accommodates smaller pieces of wood; thus it becomes a
question of preference between a greater depth which permits the use of
large logs that burn longer and a shallower depth (fig. 28, _A_ and _B_)
which takes smaller-sized wood but throws out more heat.
In small fireplaces a depth of 12 inches will permit good draft if the
throat is constructed as explained above, but a minimum depth of 16 to 18
inches is advised to lessen the danger of brands falling out on the floor.
As a rule, fireplaces on the second floor are smaller than those on the
first floor and it is well to follow this practice because the flue
height is less for second floor fireplaces (fig. 29).
Unless a fireplace 6 feet wide is fully 28 inches deep, the logs will
have to be split, and some advantage of the wide opening will be lost.
Screens of suitable design should be placed in front of all fireplaces
(fig. 30).
[Illustration: Figure 27.--This inexpensive fireplace 32 inches square
shows how a plain brick front can be used in a small room.]
A fireplace 30 to 36 inches wide is generally suitable for a room having
300 square feet of floor (fig. 31). The width should be increased for
larger rooms, but all other dimensions should be taken from table 3 for
the width selected.
The corner of a room often is the favorite location for a fireplace (fig.
32). Fireplaces of the type shown in figure 28 are also built in corners.
[Illustration: Figure 28.--A, A shallow fireplace, with a copper hood,
built as shown in B, throws out considerable heat after the hood gets
hot. The wall should be of fire-resistant masonry.]
[Illustration: Figure 29.--This shallow fireplace with a sloping back is
a type that was frequently built in bedrooms before the general use of
stoves. Note the neat and well-proportioned mantel.]
[Illustration: Figure 30.--Screens are almost essential to protect the
upholstery of nearby furniture from sparks. This fireplace shows artistic
use of small stones and makes a pleasing contrast with the log walls.]
Units providing for burning gas are often built in to resemble fireplaces
(fig. 33).
Pleasing designs result from exercising good taste in use of materials
and mantels that suit the room. The photographs in this bulletin have
been selected to illustrate various architectural effects that can be
developed and should help in the choice of a type suitable for houses of
different designs. The essentials for safety and utility, however, should
not be sacrificed for style.
[Illustration: Figure 31.--This 36-inch-wide fireplace does not seem too
large for the small room, but its size would have been accentuated by the
use of a mantel.]