Wall Shield Required Where |
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Less Than 12". Adjacent Wall Is |
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| Hearth Extension Dimensions | ||
Never Allowed Closer Than 7". |
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24" |
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| A | 16" |
Protected |
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| B | 30" |
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Side Wall |
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30" |
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| D | 46" |
C | C | B | C | Note: To convert inches to millimeters divide by .03937. | |
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B |
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D |
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C | A |
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| Figure 42 |
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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 5.
Using the k formula:
Minimum |
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thickness of | = | alternate material (kM) | x | thickness | |||||
alternate |
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material (TM) |
| of listed material (kL) |
| material (TL) | |||||
TM (inches) | = |
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| kM |
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| *.84 |
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TM (inches) | = |
| *.35 |
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*.84 |
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.416 (inches)= |
| .416 |
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Answer - The minimum required thickness of the Micore 160 is .417," there- fore round up to nearest standard thickness available which is 1/2."
Listed Material
| k (per inch) | r (per inch) | Listed Min.Thickness | |
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Listed Material | .84 | 1.19 | 1" | |
| KL | rL | T | L |
** Approved Alternate Materials for Floor/Hearth Protection | ||||
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AlternativeMaterials | Thermal Values | MinimumThickness | ||
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| k (per inch) | r (per inch) | Min. Thickness | |
| KM | rM | TM | |
Kaowool M Board | .47 | 2.13 | .56" (1/2") | |
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Micore 160™ | .35 | 2.86 | .42" (3/8") | |
U.S. Gypsum |
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Micore 300™ | .46 | 2.17 | .55" (1/2") | |
U.S. Gypsum |
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Durock™ Cement Board | 1.92 | .52 | 2.29" | |
U.S. Gypsum |
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Hardibacker™ | 1.95 | .513 | 2.32" | |
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Hardibacker 500™ | 2.30 | .435 | 2.74" | |
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Cultered Stone Hearth- | 2.82 | .355 | 3.36" | |
stone™ |
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Wonderboard | 3.23 | .31 | 3.85" | |
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Super Firetemp M | .61 | 1.64 | .73" (3/4") | |
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Super Firetemp L | .54 | 1.85 | .64" (5/8") | |
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Face brick | 9.00 | .111 | 10.71" | |
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Common brick | 5.00 | .20 | 5.95" (6") | |
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Cement mortar | 5.00 | .20 | 5.95" (6") | |
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Ceramic tile | 12.5 | .08 | 14.88" | |
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Marble | ~11 | ~.09 | 13.10" | |
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Using the r formula:
Minimum thickness of = alternate material
TM (inches) | = |
rL
rM
Specified min.
xthickness of listed material
xTL
Table 5 |
**If the hearth extension material(s) that is intended to be used is NOT listed on Table 5, the material can still be used if the material(s) is noncombustible. However, the manufacturer of the material must provide either the listed
Note: Also see NFI (National Fireplace Institute) Certification Manuals showing other exceptable caluculation methods and acceptable alternate materials which can be used.
TM (inches) | = | *1.19 | x | 1" | |
* 2.86 | |||||
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.417 (inches)= |
| .416 | x | 1" |
Answer - The minimum required thickness of the Micore 160 is .417," there- fore round up to nearest standard thickness available which is 1/2."
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
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