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8Finishing
A. Hearth Extension
A hearth extension must be installed with all fi replaces to protect the combustible fl oor in front of the fi replace from both radiant heat and sparks. See Figures
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HX3 or HX4 | 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 equivilent |
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(see Table below) |
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| Metal Hearth |
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| Strip |
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| 2 in. (51 mm) |
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Floor constructed of wood or | required |
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| 1 in. (25 mm) overlap | ||
other combustible material |
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Figure 8.1 Hearth Extension Construction |
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| Metal strips are placed 2 in. (51 mm) under the | |
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| front of the fireplace and must extend beyond the | |
| WARNING |
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| front and sides of fireplace by 2 in. (51 mm). | ||
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| Figure 8.2 Positioning the Protective Metal Hearth Strips | |||
| Fire Risk |
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| • Metal hearth strips MUST be installed. | WARNING | ||||
| Sparks or embers may ignite fl ooring. | |||||
This fi replace has been tested and approved for use with a | Fire Risk | |||||
• Hearth extensions must be installed | ||||||
hearth extension insulated to a minimum R value of 1.16. | ||||||
exactly as specifi ed. | ||||||
To substitute materials for the | ||||||
High temperatures or hot embers may ignite | ||||||
tensions, see Figure 8.3 and calculate insulation alternatives | concealed combustibles. | |||||
as per Table 8.1 and the following formulas: |
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•Thermal conductivity per inch thickness = k
•k = (BTU)(inch) / (foot2)(hour)(°F)
•Required thickness = Rk
•Thermal resistance per inch thickness = r
•r = (foot2)(hour)(°F) / (BTU)(inch)
•Required thickness = R / rB.
Table 8.1 |
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Hearth Extension Insulation Alternatives, R Value = 1.16 |
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| Minimum |
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| k per inch | r per inch | thickness |
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| Model # | A | B | C |
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Material | thick | thick | required |
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Hearth & Home HX3, HX4 | 0.43 | 2.33 | 1/2 in. |
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| HX4 | in. | 66 | 20 | 12 |
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USG Micore 300™ | 0.46 | 2.18 | 1/2 in. |
| mm | 1676 | 508 | 305 |
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USG Durock™ Cement Board | 1.92 | 0.52 |
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Cement Mortar | 5.0 | 0.20 |
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Common Brick | 5.0 | 0.20 |
| Figure 8.3 Hearth Extension Dimensions | |||||||
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Ceramic Tile | 12.50 | 0.08 |
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Armstrong™ Privacy Guard Plus | .046 | 2.18 | 1/2 in. |
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Marble |
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24 | Heatilator • ST42A • 35038 Rev G • 02/05 |