Firebox of prefabricated blocks, assemblage therefor and method of assembly

Fifteen prefabricated refractory concrete blocks, consisting of ten different sizes and/or shapes assemble to provide a replacement firebox of U-shape with facing side walls joined by a rear wall. In one embodiment a metal lintel is disposed at the front upper boundary of the structure produced from the fifteen blocks, the lintel resting on the side walls bridging the opening therebetween and defining the upper boundary of the hearth opening. A masonry transition cone is erected atop the side walls and lintel. In a second embodiment, trapezoidal sheet metal panels are assembled to form a transition cone above the U-shape structure. The bottom courses are produced from blocks that are in the form of oblique rectangular parallelepipeds. These are arranged so that the joints are staggered vertically. The upper portion of the rear wall below the transition cone is formed from oblique trapezoidal prismatic blocks. Certain of the blocks in addition are truncated.

BACKGROUND OF THE INVENTION 
The present invention relates to a firebox for an open hearth fireplace 
and, more particularly, primarily to a replacement firebox for 
deteriorated metal fireboxes. 
For many years, various metal fireplace units have been used by builders to 
facilitate fireplace construction. Such units, referred to in the trade as 
"Builder Boxes", provide a functionally effective design providing a form 
easily surrounded by masonry, faced with masonry veneer, and surmounted by 
a chimney. Highly skilled masons knowledgeable in fireplace construction 
are not needed and much of the guesswork is eliminated from the 
construction of masonry fireplaces. Unfortunately, metal fireboxes are not 
durable and depending upon climatic conditions and the nature of the wood 
burned therein rarely last as long as 25 years, and generally fail on 
average within seven to ten years. 
When a metal firebox fails, a result of metal corrosion, the fireplace is 
unusable until the defect is corrected. Several corrective methods have 
heretofore been employed. One procedure involves cutting away the 
rusted-out or deteriorated area in the firebox and welding in a new piece 
of sheet metal. This remedy is only temporary because the same area is 
likely to rust-out again, and other faults are likely to develop. 
Another procedure is to tear down the entire fireplace and rebuild it with 
a more durable type. This represents a very expensive alternative. Yet 
another procedure involves cutting the metal firebox out of the 
surrounding masonry and replacing it with a masonry liner of firebrick. 
This is difficult and labor intensive, and there is a tremendous shortage 
of masons capable of this type of construction. 
In U.S. Pat. No. 4,470,399, issued Sept. 11, 1984 for "Fireplace 
Construction" there is disclosed and claimed a fireplace comprising a 
stacked plurality of courses of modular prismatic blocks laid upon a base 
to define a firebox region of opposed side walls and a rear wall 
contiguous thereto. The blocks are of cast refractory concrete, and the 
patented fireplace employs specially configured blocks for establishing 
serpentine flue passages and a heat exchange air circulatory system. 
It is, therefore, an object of the present invention to provide a simple 
and readily installable replacement firebox for a deteriorated metal 
firebox. 
Another object is to provide a masonry replacement for the metal firebox of 
an existing fireplace which replacement is easy to install and which is 
not dependent upon highly skilled masons. 
Yet another object of the present invention is to provide an inexpensive 
replacement firebox for a deteriorated metal firebox. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the present invention there is provided a 
firebox for an open hearth fireplace comprising an assemblage of 
prefabricated modular masonry components in which a plurality of courses 
of refractory concrete blocks are superposed one above the other to the 
height of the hearth opening forming a U-shape first structure with facing 
side walls joined by a rear wall, and a transition cone located atop said 
first structure for interconnecting said first structure with a chimney, 
said first structure having side walls of uniform thickness which diverge 
in the forward direction from said rear wall, said rear wall having a 
lower portion of uniform thickness and vertical surfaces, and having an 
adjacent upper portion wherein the inner surface is inclined forwardly in 
the upward direction, and said transition cone has a front inner surface 
that is inclined rearwardly in the upward direction. 
In accordance with a further aspect of the present invention there is 
provided a method for replacing metal fireboxes in an open hearth 
fireplace which comprises in combination the steps of removing the metal 
firebox, inspecting and performing any needed repair to the existing 
hearth slab, assembling with refractory mortar on said hearth slab a 
plurality of courses of prefabricated refractory concrete blocks, laying 
one course above the previous course to the height of the hearth opening 
and forming thereby a U-shape first structure with facing side walls 
joined by a rear wall, and disposing a transition cone between said first 
structure and an existing chimney, said first structure having side walls 
of uniform thickness which diverge in the forward direction from said rear 
wall, said rear wall having a lower portion of uniform thickness and 
vertical surfaces, and having an adjacent upper portion wherein the inner 
surface is inclined forwardly in the upward direction, and said transition 
cone has a front inner surface that is inclined rearwardly in the upward 
direction. 
Finally, in accordance with yet another aspect of the present invention 
there is provided an assemblage of prefabricated refractory concrete 
blocks for erecting a firebox for an open hearth fireplace, said 
assemblage comprising ten differently sized and shaped blocks, some of 
which blocks are duplicated to provide at least fifteen of said blocks 
which when laid in courses of three blocks each produce a U-shape 
structure with facing side walls joined by a rear wall, said blocks being 
shaped to form said side walls with uniform thickness diverging in the 
forward direction, and structural members for erecting a transition cone 
to surmount said U-shape structure.

The same reference numerals are used throughout the drawings to designate 
the same or similar component. 
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
Referring to the drawings, and particularly to FIG. 1, there is shown a 
brick faced fireplace 10 having a hearth 11, and brick veneer face 12 
topped by a mantel 13, and a metal firebox consisting of a series of 
panels of which two side panels 14 and 15, a rear panel 16, and a bottom 
panel 17 are visible. Shown in phantom lines is the outline of a chimney 
18. 
As illustrative of the deterioration of the metal firebox, the panels are 
shown to contain corroded areas 19, and the panel 14 is shown 
schematically as in the process of being removed. After the entire metal 
firebox is removed, it is replaced by a firebox in accordance with the 
present invention, the renovated fireplace being shown in FIG. 2 having a 
reconstructed hearth of firebrick 20 and walls 21 of prefabricated 
concrete refractory blocks. 
Reference now should be had to FIGS. 3, 4 and 5 showing the fully assembled 
refractory block firebox in relation to the chimney 18 and to the face 
brick veneer 12 above the fireplace opening. The various numerals within a 
circle associated with the various blocks identify the figure of the 
drawings that shows the particular block in detail. 
The masonry firebox consists of two principal sections, one of which is 
further divisible into two sub-sections. Thus, it will be seen that the 
firebox, designated generally by the reference numeral 25, is formed from 
an assemblage of prefabricated modular masonry components in which a 
plurality of courses of the refractory concrete blocks are superposed one 
above the other to the height of the hearth opening forming a U-shape 
first structure 26 with facing side walls 27 and 28 joined by a rear wall 
29. In this embodiment a metal lintel, for example the steel angle iron 
30, is disposed at the front upper boundary of the hearth opening. 
Additional courses of prefabricated modular refractory concrete blocks, 31 
and 32, are supported by the lintel 30 and the first structure 26 and 
provide a masonry transition cone 33 between the first structure 26 and 
the chimney 18. The side walls 27 and 28 of the first structure 26 are of 
uniform thickness throughout and diverge in the forward direction from the 
rear wall 29. The rear wall 29 has a lower portion 34 of uniform thickness 
and vertical surfaces, and an adjacent upper portion 35 wherein the inner 
surface 36 is inclined forwardly in the upward direction. Also, the 
transition cone 33 has a front inner surface 37 that is inclined 
rearwardly in the upward direction. 
Referring to FIG. 9, the various courses of masonry blocks that 
collectively form the firebox 25 are shown in an exploded view with the 
first or bottommost course illustrated in the lower right section of the 
drawing above the figure designator, while the topmost course appears in 
the upper lefthand corner of the drawing. Starting with the first course, 
it is formed from three Prefabricated blocks 40, 41 and 42 which blocks 
are illustrated in greater detail in FIGS. 11, 12 and 13, respectively. 
Three blocks, identical to those in the first course, are arranged in the 
reverse order above the first course to produce the second course. To 
distinguish the blocks the reference numerals of the second course are the 
same as those used for the blocks of the first course with the exception 
that the letter "a" has been added to the number. Thus, the second course 
is shown as formed from blocks 40a, 41a, and 42a. Similarly, the third 
course consists of blocks 40b, 41b, and 42b. By reversing the order of the 
blocks in the first three courses, the joints are staggered in the 
vertical direction. A similar scheme is followed in numbering the 
remaining blocks in FIG. 9; where the block repeats, a letter is added to 
the numeral for purpose of separate reference. The numerals within the 
circles identify other figures of the drawings showing the respective 
block in greater detail. FIGS. 10A, 10B, 10C and 10D show in exploded form 
the blocks for the four upper courses of the structure 26. 
Directing attention to FIG. 11, the block 40 is shown as having a 
rectangular cross-section and oblique or mitered end faces 60 and 61. The 
face 62 is rhomboid, the face 63 is rectangular as well as the opposite 
face 64. The bottom face 65 is also rhomboid. Thus, the block 40 is a true 
oblique rectangular parallelepiped if its smaller area end face 60 or 61 
is considered the prism base. 
Block 41 is shown in FIG. 12. The opposing faces 66 and 67 are rectangular 
while opposing faces 68 and 69 take the form of an equiangular trapezoid. 
The cross-section is rectangular. Consequently, block 41 can be classified 
as a truncated oblique rectangular prism or parallelepiped where the end 
face 70 or 71 is considered the base of the prism. 
FIG. 13 illustrates block 42, it is similar to the block 40 although not as 
long, it being shorter by the width of block 41 measured normal to the 
faces 66 and 67. Block 42 is a true oblique rectangular parallelepiped, 
following the manner adopted for classifying the shape. 
Block 43 shown in FIG. 14 is an oblique trapezoidal prism that has been 
truncated. Thus, in cross-section block 43 is trapezoidal, the block face 
72 being beveled as best seen in FIG. 4 in order to provide the inclined 
firebox surface 36. In plan, the face 73 of block 43 is an equiangular 
trapezoid, as well as the bottom face 74. The faces 72 and 75 are both 
rectangular. 
Blocks 44 and 45, shown in FIGS. 15 and 16, respectively, are similar to 
block 43 although wider in cross-section as evident from FIG. 4. These 
blocks are, therefore, oblique trapezoidal prisms that have been 
truncated. Again, it is assumed that one of the smaller ends corresponds 
to the base of the prism. 
Blocks 46 and 47, shown in FIGS. 17 and 18, are somewhat more complex. 
Generically, they can be classified as truncated oblique rectangular 
prisms. They are both rectangular in cross-section. The end faces 76 and 
77 are rectangular and may be thought of as the base of the prism. These 
faces are formed as a simple miter or bevel. However, the opposite end 
faces 78 and 79, respectively, are provided at a compound miter angle to 
mate with the sloping faces of blocks 43 and 44, respectively. For similar 
reason the end face 80 of block 48 is provided at a compound miter angle. 
See FIG. 19. The front edges 81 and 82 of blocks 48 and 49 are stepped or 
relieved in order to accommodate the lintel 30. Blocks 19 and 20 are in 
the form of oblique rectangular prisms, the block 48 being truncated, and 
both blocks having the stepped region, as shown. 
Recapitulating, it should now be evident that the refractory concrete 
blocks in that part of the first structure 26 that includes the rear wall 
lower portion 34, are all in the form of oblique rectangular 
parallelepipeds. The upper portion 35 of the rear wall is formed from 
oblique trapezoidal prismatic blocks. The side walls 27 and 28 are formed 
from oblique rectangular parallelepiped blocks. There are ten differently 
sized and shaped blocks, the details of which are shown in FIGS. 11 to 20, 
respectively, from which the structure 26 is constructed. Some of the 
blocks, i.e., the blocks 40, 41 and 42 illustrated in FIGS. 11, 12 and 13, 
are duplicated to provide the fifteen blocks, laid in courses of three 
blocks each, that produce the U-shape structure 26. All of the duplicated 
blocks are in the shape of oblique rectangular parallelepipeds. In the 
illustrated embodiment there are five of the FIG. 11 block of a first 
size, three of the FIG. 13 block of a second size, and three of the FIG. 
12 block of a third size, the latter also being truncated. The three 
truncated oblique trapezoidal prisms 43, 44 and 45 are of differing 
cross-sectional size as clearly evident from FIG. 4. 
In order to produce a standard firebox replacement, the overall dimensions 
of the blocks in inches are as shown in the following table, the location 
of the height H, width W, and length L dimensions being typically shown in 
FIG. 11. 
______________________________________ 
FIG. Block No. H W L 
______________________________________ 
11 40 6 41/2 233/8 
12 41 6 41/2 297/8 
13 42 6 41/2 18 15/32 
14 43 6 61/2 311/8 
15 44 6 81/2 32 11/32 
16 45 6 101/2 33 19/32 
17 46 6 41/2 18 15/32 
18 47 6 41/2 163/8 
19 48 6 41/2 14 9/32 
20 49 6 41/2 233/8 
______________________________________ 
A satisfactory lintel is provided by a steel angle iron 
3".times.3".times.1/4" having a length of 45". This provides a hearth 
opening approximately 36" wide and 34" high with an interior depth of 
about 161/2". A modified embodiment is contemplated in which the lowermost 
course consisting of blocks 40, 41 and 42, is omitted. This will produce a 
firebox opening 28" high and 36" wide. 
The blocks forming the transition cone 33 are each 75/8" high, the course 
31 producing a trapezoidal structure 403/8" wide at the front, 281/8" wide 
at the rear, and 20" deep. The course 32 produces a trapezoidal structure 
27 15/16" wide at the front, 17" wide at the rear and 17 11/16" deep. With 
the rear wall flush from top to bottom of the structure the course 31 is 
set back 1" from the front of the lintel 30 while the course 32 is set 
back 2 5/16" from the front surface of course 31. The opening 100, see 
FIG. 3, at the top of the course 32, is approximately 11".times.11" to tie 
in with a standard size chimney for this size firebox. All of the blocks 
in courses 31 and 32 are provided with tongue and groove joints as shown. 
The slope of the front wall 37 (see FIG. 4) is 2" in 75/8". 
All of the blocks are produced from a lightweight aggregate with "Lumnite" 
cement as a binder. 
In a typical replacement situation, the worn metal firebox is removed. 
After inspecting and performing any needed repair to the existing hearth 
slab, the assemblage of prefabricated blocks are initially placed in 
position without mortar to ensure proper fit. Usually, some slight gap 
will exist between the top of the transition cone and the flue or chimney. 
However, during final erection this will be filled with conventional 
firebrick. The loosely assembled firebox is then disassembled and re-laid 
setting in refractory mortar and filling space behind blocks with 
refractory mortar and, if necessary, refractory brick. As mentioned above, 
the top course 32 will probably stop short of the flue and is then topped 
off with refractory brick. 
In the embodiment described above, masonry blocks are used to produce the 
transition cone 33. However, there are installations where a structurally 
self-sustaining transition cone susceptible of at least some shape and 
dimensional adjustment is preferable or desirable. For this purpose, the 
modified embodiment illustrated in FIGS. 21 and 22, can be used 
advantageously. As shown in FIG. 21, the bottom section of the firebox can 
be identical with the section 26 shown in FIGS. 3 to 5, with the exception 
that the steel lintel 30 is no longer required and, consequently, the 
blocks 48 and 49 are modified to omit the stepped recesses 81 and 82 (see 
FIGS. 19 and 20) that were provided to accomodate the lintel. In addition, 
FIG. 21 is illustrated as consisting of five courses of blocks, the 
bottommost course having been omitted. 
The embodiment of FIG. 21 is provided with a stainless steel sheet metal 
transition cone 233 having the general configuration of a frustrum of a 
right rectangular pyramid. The cone, as seen in FIG. 22, is constructed by 
assembling front, back and side panels, 234, 235, 236 and 237, 
respectively, with stainless steel nuts, bolts and lock washers. Extender 
clips 238 are provided to provide an adjustable bridge between the cone 
structure and the existing flue or chimney. 
To install the structure of FIGS. 21 and 22, the cone is loosely assembled 
and located as to proper installation height by stacking on top of an 
initial mortar-free stack of the blocks forming the bottom masonry 
structure. After adjusting for proper fit, the seams in the cone are 
caulked and the exterior is covered with a layer of glass wool insulation 
cemented to the metal. This has not been illustrated in the drawings. The 
cone is then suspended in the fireplace opening above the hearth in 
communication with the flue while the U-shaped masonry block structure is 
erected beneath it on the hearth. The components are mortared into place, 
and the top course is cemented to the base of the cone 233 with a suitable 
adhesive. The extension clips are then adjusted to contact the bottom of 
the flue and sealed thereto with suitable adhesive. 
While the modular fireplace construction described herein is ideally suited 
to replacing existing firebox liners, the embodiment described with 
reference to FIGS. 1 to 20, utilizing a masonry transition cone, can be 
used advantageously with new construction. The base and transition cone 
provide adequate support for erecting a chimney thereover. Actually, the 
metal cone can also be used with original construction if suitable support 
can be provided for construction of the chimney. But an all masonry 
construction is preferred in this situation. 
Having described the present invention with reference to the presently 
preferred embodiments thereof, it should be apparent to those skilled in 
the subject art that various changes in construction can be introduced 
without departing from the true spirit of the invention as defined in the 
appended claims.