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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
22
LENNOX HEARTH PRODUCTS • ESTATE™ SERIES WOOD-BURNING FIREPLACES • MODELS EST-36, EST-42, EST-50 • INSTALLATION INSTRUCTIONS
Table 1
**If the material intended to be used for the hearth extension is not listed in the
above table, the material can still be used if it is noncombustible. To calculate the
minimum required hearth thickness (per the instructions on this and the previous
page and/or as specified in the NFI Certification manuals), the material manufacturer
must provide either the listed k-value per inch or r-value per inch with listed
thickness.
NOTE: Also see NFI (National Fireplace Institute) Certification Manuals for
other acceptable calculation methods and acceptable alternate materials
that can be used.
LISTED MATERIAL
k (per inch) r (per inch) Listed Min.Thickness
Listed Material .84
k
L
1.19
r
L
1
"
T
L
APPROVED ALTERNATE MATERIALS FOR FLOOR/HEARTH PROTECTION**
Alternate Materials Thermal Values
MinimumThickness
(rounded to nearest 1/8 inch)
k (per inch)
k
M
r (per inch)
r
M
Min. Thickness
T
M
Kaowool M Board .47 2.13 .56" (1/2")
Micore 160™
U.S. Gypsum
.35 2.86 .42" (3/8")
Micore 300™
U.S. Gypsum
.46 2.17 .55" (1/2")
Durock™ Cement Board
U.S. Gypsum
1.92 .52 2.29" (2-1/4")
Hardibacker™ 1.95 .513 2.32" (2-3/8")
Hardibacker 500™ 2.30 .435 2.74" (2-3/4")
Cultered Stone
Hearthstone™
2.82 .355 3.36" (3-3/8")
Wonderboard 3.23 .31 3.85" (3-7/8")
Super Firetemp M
Johns-Manville
.61 1.64 .73" (3/4")
Super Firetemp L
Johns-Manville
.54 1.85 .64" (5/8")
Face brick 9.00 .111 10.71" (10-3/4")
Common brick 5.00 .20 5.95" (6")
Cement mortar 5.00 .20 5.95" (6")
Ceramic tile 12.5 .08 14.88" (14-7/8")
Marble 11 .09 13.10" (13-1/8")
Table 1
Wall Shield
Required if
less than
18" (457mm)
40"
(1016mm)
40"
(1016mm)
C
C
B
A
Figure 48
Calculating Minimum Thickness if Multiple
Materials are Used
At times it is important to know what
combination of materials are acceptable for use
as floor protection. The “R values” are used to
determine acceptable combinations of materials
because “R values” are additive where r and k
values are not.
“R value” = 1/k = “r” x thickness of mate-
rial used
Example: Given that the required “R value” for
a suitable floor protector used must be equal
to or greater than:
“R” = r
L
x T
L
= 1.19 x 1" = 1.19".
If it is desired to elevate a marble hearth exten-
sion to a level of 5" or more above the floor
surface. What combination of noncombustible
materials can be used to accomplish this?
If common brick is used so that the 3 1/2"
dimension is the height, “R” for the common
brick becomes:
brick
“R”
M
= r
M
x T
S
= 0.20 x 3 1/2" = .70
Using 1/2" of mortar to set the brick, “R” for
the mortar is calculated as follows:
mortar
“R”
M
= r
M
x T
S
= 0.20 x 1/2" = .10
Next, a 3/4" marble slab set in 1/2" mortar cov-
ers the brick, “R” for the marble and mortar
becomes:
marble
“R”
M
= r
M
x T
S
= 0.05 x 3/4" = .038
mortar
“R”
M
= r
M
x T
S
= 0.20 x 1/2" = .10