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Using the k formula:
Desired
k value of desired
Required = material (per inch) x of Listed
Thickness
k value of listed
material (per inch)
T
(Inches) = k
x T
M
m
L
.84
T
(inches) = 0.43* x 1" **
M
.84
Answer using k = 0.51 x 1" = 0.51 =
Using the r formula:
Desired
r value of listed
Required = material (per inch) x of Listed
Thickness
r value of desired
material (per inch)
T
(inches) = 1.19 x T
M
L
r
M
T
(inches) = 1.19
x 1"**
M
2.33*
Answer using r = 0.51 x 1" = 0.51 =
Alternative Hearth Extension
and Wall Shield Materials
Listed
Values
Material
k
r
Millboard
0.84
1.19
Alternative
Values
Materials
k
r
Common brick
5.00
0.20
Cement mortar 5.00
0.20
Ceramic tile
12.5
0.08
Marble
11.0
0.09
Micore CV230
0.43
2.33
(U.S. Gypsum)
Ceraform 126
0.27
3.70
(Johns-Manville)
At times it is important to know what combina-
tions of materials are acceptable for use as
hearth extensions. The "R values" are used to
determine acceptable combinations of materi-
als because "R values" are additive where r and
k values are not.
"R value" = 1 = r x thickness of material used
Min. thickness
Example: Given that the required "R value" for
a suitable hearth extension used with the
Material
TM-4500 be equal to or greater than "R" = r x T
= 1.19 x 1" = 1.19. It is desired to elevate a
marble hearth extension to a level of 6
more above the floor surface. What combina-
tion of noncombustible materials can be used
to accomplish this?
If two common bricks are used so that the 3 "
flat dimension is the height, "R" for the com-
".
mon brick becomes:
"R"
= r x T
M
Min. thickness
Using " of mortar to set the brick, "R" for the
mortar becomes:
Material
"R"
= r x T
M
A
" marble slab set in
brick, "R" for the marble and mortar becomes:
"R"
= r x T
M
"R"
= r x T
M
"
The sum of all "R values" is:
1.1 + .05 + .068 + .05 = 1.268
This would be an acceptable combination of
Min. Thick
material for the hearth extension since the total
calculated "R value" of the materials used ex-
T
L
ceeds the required "R value" of 1.19.
1"
WARNING: THE CRACK BETWEEN THE
Min. Thick
FIREPLACE AND THE HEARTH EXTEN-
T
SION MUST BE SEALED WITH A NON-
M
COMBUSTIBLE MATERIAL.
6"
6"
WARNING: WHEN INSTALLING THE
HEARTH EXTENSION, BE CAREFUL NOT
15"
TO BLOCK THE LOWER HEAT-CIRCULAT-
13"
ING AIR GRILL ON MODEL TMC-4500.
"
WARNING: FIREPLACE MUST BE RAISED
IF HEIGHT OF HEARTH EXTENSION EX-
"
CEEDS 7" (178 MM) FOR THE TM-4500
OR 2
" (60 MM) FOR THE TMC-4500
( FIGURES 57 AND 58 ).
* value taken from chart
** minimum thickness per listing
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
k
" or
= 0.20 x 5
" = .1.10
M
= 0.20 x
"
= .05
M
" mortar covers the
= 0.09 x
"
= .068
M
= 0.20 x
"
= .05
M
L
7" Max.
(178mm)
Max. Thickness of Hearth Extension
when TM Fireplace is on the Floor
Figure 57
2
" Max.
(60mm)
Max. Thickness of Hearth Extension
when TMC Fireplace is on the Floor
Figure 58
FINISH TO YOUR TASTE
There are a wide variety of "finished looks" for
your TM and TMC Series from formal wall
decor with elaborate mantels to rustic wood
paneling or warm brick facings.
Only noncombustible materials like stone, tile,
brick, etc. may overlap the black front facing,
but be sure not to interfere with the installation
and operation of glass doors or block the lower
air grille on the TMC-4500. Seal all joints be-
tween the black facing and wall surrounds to
prevent air intrusion. Use noncombustible caulk-
ing material only to seal the black metal facing
to the surround material on the finished wall.
Combustible materials may project beyond the
sides of the fireplace opening as long as they
are kept within the shaded areas illustrated in
Figure 59 .
Combustible
Materials Allowed
in Shaded Areas
3
"
(83mm)
4
"
15
(121mm)
Figure 59
Fireplace
"
(13mm)
12" (305mm)
Min. Distance to
Protected Side Wall
18" (457mm)
Min. Distance to
Unprotected Side Wall
17
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