7100FP EPA Woodburning Fireplace
8 Finishing
A. Hearth Extension
A hearth extension must be installed with all fireplaces to protect the combustible floor in front of the fireplace from both radiant heat and sparks. See Figures 38.1 below, and Figures 39.1 and 39.2 on page 39.
| High temperature |
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| (300°F min.) continuous, |
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HX3 or HX4 | Fireplace |
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Protective | |||||
insulation | |||||
Hearth Ext | Tile, stone or other |
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or equivalent |
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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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other combustible material |
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Figure 38.1 Hearth Extension Construction
WARNING
Fire Risk
•Maintain clearances.
•Use only
•Framing or finishing material used on the front of, or in front of, the appliance closer than the minimums listed, must be constructed entirely of noncombustible materials (i.e., steel studs, concrete board, etc.).
B.Calculating Alternate Floor Protection Material
Thermal Conductivity: k value
The k value indicates the amount of heat (in BTU’s) that will flow in 1 hour through 1 square foot of a uniform material 1 inch thick for each degree (F) of temperature difference from one side of the material to the other. The LOWER the k factor means less heat is being conducted through the
(BTU) (inch) (foot2 (hour) (oF)
Thermal Resistance: R value
The R value is a measure of a material’s resistance to heat transfer. R value is convenient when more than one material is used since you can add the R values together, whereas you can not do this for k value. The HIGHER the R
R
factor means less heat is being conducted through the non- combustible material to the combustible material beneath it. The R value of a material must be equal or larger then the required R value to be acceptable.
Converting k to R:
Divide 1 by k and multiply the results times the thickness in inch- es of the material.
R = 1/k x inches of thickness
Converting R to k:
Divide the inches of thickness by R. k = inches of thickness/R
Calculations:
Example: Floor protection requires k value of 0.84 and 3/4 inch thick.
Alternative material has a k value of 0.6 and is 3/4 inch thick.
Divide 0.6 by .75 = k value of 0.80. This k value is smaller than 0.84 and therefore is acceptable.
Table 38.2
Hearth Extension Insulation Alternatives, R Value = 1.16
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Material | k per inch | R per inch | thickness |
thick | thick | required | |
Hearth & Home HX3, HX4 | 0.49 | 2.18 | 1 in. |
USG Micore 300™ | 0.49 | 2.18 | 1 in. |
USG Durock™ Cement Board | 1.92 | 0.52 | |
Cement Mortor | 5.0 | 0.20 | |
Common Brick | 5.0 | 0.20 | |
Ceramic Tile | 12.50 | 0.08 | |
Armstrong™ Privacy |
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Guard Plus | 0.046 | 2.18 | 1/2 in. |
Marble |
Page 38 | September 7, 2007 |