NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
16
Figure 43
A
B
D
C
C
Hearth Extension Dimensions
(For
Figures 43 and 44 )
A
20"
B
41"
C
12"
D
65"
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.
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
M
= k value per inch of
alternate
material
r
M
= r value per inch of
alternate
material
T
M
= minimum thickness required for
alternate
material
T
S
= standard thickness of the
alternate
material
k
L
= k value per inch of
listed
material
r
L
= r value per inch of
listed
material
T
L
= minimum thickness of
listed
material
Note:
An asterix “
*
” indicates, it is a value taken from
Table 1
.
Using the k formula:
Minimum
k-value (per Inch) of
Specified min.
thickness of
=
alternate material (k
M
) x
thickness
alternate
k-value (per inch)
of listed
material (T
M
)
of listed material (k
M
)
material (T
L
)
T
M
(inches)
=
k
M
x
T
L
*.84
T
M
(inches)
=
*.35
x
1"
*.84
.416 (inches) =
.416
x
1"
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)
Specified min.
thickness of
=
of listed material
x
thickness
alternate
r-value (per inch)
of listed
material
of alternate material
material
T
M
(inches)
=
r
L
x
T
L
r
M
T
M
(inches)
=
*1.19
x
1"
*2.86
.416 (inches) =
.416
x
1"
Figure 44
Wall Shield Required
Where Less Than 15"
A
B
C
C
36”
24”
D
