Lennox Hearth Products MERIT MP-36OD Installation Instructions Manual page 21

Wall Shield Required
Where Less Than 12"
24"
30"
C
B
D
C
Methods of Determining Hearth Extension and Wall Shield
Equivalents -
To determine the thickness required for the alternate
material when either the "k" value or "r" value is known, use either the
k formula or r formula.
Example: If Micore 160 is to be used for the hearth extension fi replace,
how thick must this material be?
k = k value per inch of alternate material
M
r = r value per inch of alternate
M
T = minimum thickness required for alternate material
M
T = standard thickness of the alternate material
S
k = k value per inch of listed material
L
r = r value per inch of
listed
L
T = minimum thickness of
listed
L
Note: An asterix "*" indicates, it is a value taken from Table 5.
Using the k formula:
Minimum k-value (per Inch) of
thickness of = alternate material (k
alternate k-value (per inch)
material (T ) of listed material (k
M
T (inches) =
M
T (inches) =
M
.416 (inches)=
Answer - The minimum required thickness of the Micore 160 is .417," there-
fore round up to nearest standard thickness available which is 1/2."
Using the r formula:
Minimum r-value (per Inch)
thickness of = of listed material
alternate r-value (per inch)
material of alternate material
T (inches) =
M
T (inches) =
M
.417 (inches)=
Answer - The minimum required thickness of the Micore 160 is .417," there-
fore round up to nearest standard thickness available which is 1/2."
C
A
material
material
material
Specifi ed min.
) x thickness
M
of listed
) material (T
L
k
x T
M
L
*.84
*.35 x 1"
*.84
.416 x 1"
Specifi ed min.
x thickness
of listed
material
r
x T
L
L
r
M
*1.19 x 1"
* 2.86
.416 x 1"
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
B C
A
D
Listed Material
** Approved Alternate Materials for Floor/Hearth Protection
AlternativeMaterials
Kaowool M Board
Micore 160™
U.S. Gypsum
Micore 300™
U.S. Gypsum
Durock™ Cement Board
U.S. Gypsum
Hardibacker™
Hardibacker 500™
Cultered Stone Hearth-
stone™
)
Wonderboard
L
Super Firetemp M
Johns-Manville
Super Firetemp L
Johns-Manville
Face brick
Common brick
Cement mortar
Ceramic tile
Marble
Table 5
** If the hearth extension material(s) that is intended to be used is NOT listed
on Table 5, the material can still be used if the material(s) is noncombustible.
However, the manufacturer of the material must provide either the listed k-value
per inch or r-value per inch with listed thickness so that the minimum thickness
required for the hearth can be calculated (per instructions on this Page and/or
as specifi ed in the NFI Certifi cation manuals).
Note: Also see NFI (National Fireplace Institute) Certifi cation Manuals showing
other exceptable caluculation methods and acceptable alternate materials
which can be used.
Hearth Extension Dimensions
A
B
C
D
Note: To convert inches to millimeters divide by .03937.
Listed Material
k (per inch) r (per inch) Listed Min.Thickness
.84 1.19
r
K
L L
Thermal Values MinimumThickness
(rounded to nearest 1/8 inch)
k (per inch) r (per inch) Min. Thickness
r
K
M M
.47 2.13
.35 2.86
.46 2.17
1.92 .52
1.95 .513
2.30 .435
2.82 .355
3.23 .31
.61 1.64
.54 1.85
9.00 .111 10.71" (10-3/4")
5.00 .20
5.00 .20
12.5 .08 14.88" (14-7/8")
~11 ~.09 13.10" (13-1/8")
16"
30"
8"
46"
Figure 53
"
1
T
L
T
M
.56" (1/2")
.42" (3/8")
.55" (1/2")
2.29" (2-1/4")
2.32" (2-3/8")
2.74" (2-3/4")
3.36" (3-3/8")
3.85" (3-7/8")
.73" (3/4")
.64" (5/8")
5.95" (6")
5.95" (6")
21