Lennox Elite LA41CF Installation Instructions Manual page 16

Note: Any noncombustible material whose k
value is less than .84 or whose r value is more
than 1.19 is acceptable.
If the fireplace is installed on a combustible
floor, use the metal safety strips (provided)
on the floor extending half under the fire-
place and half under the hearth extension.
A wall shield is required where a continuous
perpendicular side wall is within 15" of the
fireplace opening ( see Figure 44 ) . Use a 40" W
x 40" H wall shield constructed of a durable,
noncombustible material having an equal or
better (lower k value) insulating value than k =
.84 BTU IN/FT 2 HR F. At no time may a
perpendicular side wall be located closer than
12" from the fireplace opening.
If fireplace is installed diagonally across a 90
corner; no wall shields are required.
Hearth Extension Dimensions
(For Figures 43 and 44 )
A
B
C
D
C
B
D
Figure 43
Wall Shield Required
Where Less Than 15"
24"
36"
C
B
D
Figure 44
16
20"
41"
12"
65"
C
A
C
A
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
Methods of Determini
ng 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 fireplace,
how thick must this material be?
k = k value per inch of alternate material
M
r = r value per inch of alternate material
M
T = minimum thickness required for alternate material
M
T = standard thickness of the alternate material
S
= k value per inch of listed material
k
L
r = r value per inch of listed material
L
T = minimum thickness of listed material
L
Note: An asterix "*" indicates, it is a value taken from Table 1 .
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) = k
M
M
*.84
T (inches) = *.35
M
*.84
.416 (inches) = .416
Answer - The minimum required thickness of the Micore 160 is .417",
therefore 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) = r
L
M
r
M
T (inches) = *1.19
M
*2.86
.416 (inches) = .416
Specified min.
) x thickness
M
of listed
) material (T )
M L
x T
L
x 1"
x 1"
Specified min.
x thickness
of listed
material
x T
L
x 1"
x 1"