If fireplace is installed diagonally across a 90° corner; no wall shields are required.
C B C
A
D
Hearth Extension Dimensions
A | 16" |
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B | 35" |
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C | 8" |
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D | 51" |
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Figure 48
Wall Shield Required
Where Less Than 12"
36"
36"
C
B
Methods of Determining Hearth Extension and Wall Shield Equivalents
To determine the thickness required for any material when either the k or r values are known:
TM | = Thickness of material in inches | |
kM | = K value of desired material | |
rM | = | R value of desired material |
TL | = | Minimum listed thickness |
Example: Micore CV230 is to be used for the hearth extension fireplace. How thick must this material be?
Using the k formula:
Desired | k value of desired | Min.thickness | |||||
Required = material (per inch) x of Listed | |||||||
Thickness | k value of listed | Material | |||||
| material (per inch) |
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TM (inches) | = |
| kM x | TL |
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| .43 |
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TM (inches) | = | 0.43* | x 1" |
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| 0.43 |
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Answer using k = 1 x 1" = 1
1" thickness Micore will be required.
Using the r formula:
Desired | r value of listed | Min.thickness | |
Required = material (per inch)x | of Listed | ||
Thickness | r value of desired |
| Material |
| material (per inch) |
| |
T (inches) | = 2.33 x T |
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“R value” = 1 = r x thickness of material used k
Alternative Hearth Extension
and Wall Shield Materials
Listed | Values | Min. Thick | |
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Material | k | r | TL |
Millboard | .43 | 2.33 | 1" |
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Alternative | Values | Min. Thick | |
Materials |
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k | r | TM | |
Wonderboard | 1.92 | 0.56 | 4 ¹⁄₄" |
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Common brick | 5.00 | 0.20 | 11 ⁵⁄₈" |
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Cement mortar | 5.00 | 0.20 | 11 ⁵⁄₈" |
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Ceramic tile | 12.5 | 0.08 | 29 ¹⁄₈" |
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Marble | 11.0 | 0.09 | 25 ⁷⁄₈" |
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Micore CV230 | 0.43 | 2.33 | 1" |
(U.S. Gypsum) |
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Ceraform 126 | 0.27 | 3.70 | ⁵⁄₈" |
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Example: Given that the required “R value” for a suitable hearth extension used must be equal to or greater than:
“R” = r x TL = 2.33 x 1" = 2.33.
If it is desired to elevate a marble hearth extension to a level of 5" or more above the floor surface. What combination of noncombustible materials can be used to accomplish this?
If common brick is used so that the 3 ¹⁄₂"
D
Figure 49
C A
M |
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| L | |
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| rM |
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TM (inches) = | 2.33 |
| x 1" | ||
2.33* |
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Answer using r = 1 x 1" = 1 =
1" thickness Micore will be required.
At times it is important to know what combination of materials are acceptable for use as hearth extensions. The “R values” are used to determine acceptable combinations of materials because “R values” are additive where r and k values are not.
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
dimension is the height, “R” for the common brick becomes:
“R”M = r x TM = 0.20 x 3 ¹⁄₂" = .70
Using ¹⁄₂" of mortar to set the brick, “R” for the mortar is calculated as follows:
“R”M = r x TM = 0.20 x ¹⁄₂" = .10
*value taken from chart
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