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/FT2 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 )
A20"
B41"
C12"
D65"
C 
B 
C 
A
D
Figure 43
Wall Shield Required
Where Less Than 15"
24” 
36”
C
B
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 fireplace, how thick must this material be?
kM = k value per inch of alternate material rM = r value per inch of alternate material
TM = minimum thickness required for alternate material TS = standard thickness of the alternate material
kL = k value per inch of listed material rL = r value per inch of listed material
TL = minimum thickness of listed material
Note: An asterix “*” indicates, it is a value taken from Table 1.
Using the k formula:
Minimum |
|
| Specified min. | ||
thickness of | = | alternate material (kM) x | thickness | ||
alternate |
|
|
| of listed | |
material (TM) |
| of listed material (kM) |
| material (TL) | |
TM (inches) | = | kM |
| x | TL |
| *.84 |
|
| ||
|
|
|
|
| |
TM (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 |
|
|
| Specified min. | ||
thickness of | = | of listed material | x | thickness | ||
alternate |
|
|
| of listed | ||
material |
| of alternate material |
| material | ||
TM (inches) | = | rL | x | TL | ||
|
| rM |
|
|
| |
TM (inches) | = | *1.19 |
|
| x | 1" |
| *2.86 |
|
|
|
| |
|
|
|
|
|
| |
.416 (inches) = | .416 |
|
| x | 1" | |
16
D
Figure 44
C A
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.