ODSHR Outdoor Woodburning Fireplace
Alternate noncombustible materials may be used pro- viding the (total) thermal resistance (Rt value) of the al- ternate material employed is greater than or equal to R
=1.09. Thermal resistance (R) or thermal conductivity (K), may be obtained from manufacturer of the material. Factors are related by the formula K = 1/R. (Fig. 28)
T = given thickness
R = thermal resistance for a given thickness (T) K = thermal conductivity
Noncombustible Decorative Covering May be Installed
or
.018" Minimum Sheet Metal
2¹⁄₂" Min.
Combustible 
Floor
Seal Cracks Between Fireplace and Hearth Extension with Non- combustible Material
Lower Sur-
roundFireplace Hearth
Noncombustible material with a lower R value may be used, provided thickness of material is sufficiently greater to maintain an equivalent (total) thermal resis- tance (Rt).
Example of Determining Hearth Extension Equivalents
To determine the thickness required for any new mate- rial:
Min. Thickness |
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(Refer to Table 4) |
| Safety Strips | |
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| Must be Over- |
Minimum Insula- | lapped 1/2" Min. | ||
tion Value |
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(Refer Table 4) | FP1169 | ||
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Seal Cracks Between Fireplace and Hearth Extension with Non- combustible Material
NEW |
| K of new material (per inch) | thickness | |
required | + |
|
| X of listed |
|
| |||
thickness |
| K of listed material (per inch) | material | |
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required thickness).
COMMON MATERIALS AND FACTORS
MATERIAL | K* | R | MINIMUM | |
THICKNESS | ||||
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|
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Lower Sur-
8" Max. round
Thickness Cement Blocks
Combustible Floor
1/4" Min.
Thickness
Minimum Insulation
Value
Fireplace
Hearth
Safety Strips Must be Over- lapped 1/2" Min.
FP1170
EH2416 | 1.09 | 0.50 in.** |
|
(CFM Corporation) 0.458 |
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Common Brick 5.0 | 0.10 | 5.46 in.** |
|
R Value is for ��� inch.
*Units of K = BTU/SQ FT/HR/˚F/IN ** Thickness of Listed Material
FP533ADD
Fig. 28 Hearth extension material factors.
Fig. 29 Protection of adjacent combustible side walls and hearth extension dimensions.
Wall Covering |
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| 2 x 4 Header |
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| |
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| - Do Not Notch |
Fig. 20 |
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| at Ledge |
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| Brackets | |
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Hearth Extension
Hearth
Extension Insulation
Molding used to Fasten Hearth Extension
in Place
Majestic Safety Strips Must | Seal Crack Between |
be Overlapped 1/2" Min. | Fireplace and Hearth |
| Extension with |
FP1171 | Noncombustible Material |
|
Fig. 30 Sealing detail.
20002264 | 17 |
