12" | Finished |
(305mm) | |
Max. | Wall |
| 1 ¹⁄₂" (38mm) |
Combustible | Noncombustible |
Mantel | |
and Trim | Wall Covering |
12" | Spacer |
(305mm) |
|
Min. |
|
6⁹⁄₁₆"
(167mm)
Fireplace
Opening
Typical Installation
Figure 46
Hearth Extensions and Wall ShieldsA hearth extension must be installed with all fireplaces. It is to protect the combustible floor in front of the fireplace from both radiant heat and sparks. The hearth extension must extend beyond the front at least 20" (508 mm) and both sides at least 12" (305 mm) (Figure 47 ). Use a hearth extension constructed of a durable noncom- bustible material having an equal or better (lower k value) insulating value of k = .84 BTU IN/FT2 HR ° F or a thermal resistance that equals or exceeds r = 1.19 HR ° F FT2/ BTU IN. With these values, determine the minimum thickness/material required using the formula and Page 17.
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 fireplace and half under the hearth extension.
A wall shield is required where a continuous perpendicular side wall is within 12" of the fireplace opening (Figure 48 ). Use a 36" W x 36" H wall shield constructed of a durable, noncombustible material having an equal or better (lower k value) insulating value than k =
.54 BTU IN/FT2 HR ° F. At no time may a perpendicular side wall be located closer than 9" from the fireplace opening.
If fireplace is installed diagonally across a 90° corner; no wall shields are required.
16
Hearth Extension Dimensions |
|
|
| |
A | 20" (508 mm) |
|
|
|
B | 36" (914 mm) |
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|
|
C | 12" (305 mm) |
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|
|
D | 60" (1524 mm) | C | B | C |
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| |||
|
|
|
| A |
|
|
| D |
|
Figure 47 |
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|
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" | |
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.