
8Finishing
A. Hearth Extension |
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A hearth extension must be installed with all fireplaces to | |||||
protect the combustible floor in front of the fireplace from | Fire Risk | ||||
both radiant heat and sparks. See Figures 8.1‑8.3. | |||||
• Metal hearth strips MUST be installed. | |||||
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| Continuous, |
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| Sparks or embers may ignite flooring. | |
1/2 in. Micore | Fireplace |
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Protective |
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insulation |
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Hearth Ext | Tile, stone or other |
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or equivalent |
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(see Table 11.2) |
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| Metal Hearth |
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| Strip |
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2 in. (51 mm)
Floor constructed of wood or required other combustible material
Figure 8.1 Hearth Extension Construction


1 in. (25 mm)
overlap
The hearth extension should slope away from the front of the |
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fireplace and chase at 1/8 in. to 1/4 in. per foot. Spark strips |
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must be used on top of any combustible hearth materials |
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Protective metal strips are placed 2 in. (51 mm) under the | |||||
used for moisture management. | |||||
front of the fireplace and must extend beyond the front | |||||
This fireplace has been tested and approved for use with a | and sides of fireplace opening by 2 in. (51 mm). | ||||
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hearth extension insulated to a minimum R value of 1.03. | Figure 8.2 Positioning the Protective Metal Hearth Strips | ||||
To substitute materials for the |
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tensions, see Figure 8.3 and calculate insulation alterna- | WARNING |
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tives as per Table 8.1 and the following formulas: |
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• Thermal conductivity per inch thickness = k | Fire Risk | ||||
• k = (BTU)(inch) / (foot2)(hour)(°F) | • Hearth extensions must be installed | ||||
• Required thickness = Rk | exactly as specified. | ||||
• Thermal resistance per inch thickness = r | High temperatures or hot embers may ignite | ||||
concealed combustibles. |
• r = (foot2)(hour)(°F) / (BTU)(inch)
• Required thickness = R / rB.
Table 8.1 |
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Hearth Extension Insulation |
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| Minimum |
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| k per inch | r per inch | thickness |
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Material | thick | thick | required |
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Hearth & Home HX3, HX4 (Micore 300™) | 0.49 | 2.06 | 1/2 in. |
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USG Micore 160™ | 0.39 | 2.54 | 1/2 in. |
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| C | |||
USG Durock™ Cement Board | 1.92 | 0.52 | 2 in. |
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Cement Mortor | 5.0 | 0.20 |
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Common Brick | 5.0 | 0.20 | CAT. # |
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Ceramic Tile | 12.50 | 0.08 |
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HX3 | in | 52 | 16 | 8 | |||||
Armstrong™ Privacy Guard Plus | 0.46 | 2.18 | 1/2 in. | ||||||
Marble |
| mm | 1321 | 406 | 203 | ||||
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| HX4 | in | 66 | 20 | 12 | |
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| mm | 1676 | 508 | 305 | |
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| Figure 8.3 Hearth Extension Dimensions |
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Outdoor Lifestyles by Hearth & Home Technologies Inc. • Montana | 23 |