Vermont Castings EWF36A
The top of insulation must be covered with a
Secure the hearth extension to the floor to prevent shifting, using trim molding or other similar means at three (3) outer edges. Seal crack between the fireplace hearth and hearth extension with a noncombustible
material. (Figs. 24 and 25)
WARNING: Hearth extension must be installed in accordance with Figure 24. Top of hearth extension must be level with bottom of fireplace.
Alternate noncombustible materials may be used providing the (total) thermal resistance (Rt value) of the alternate material employed is greater than or equal to R = 1.09 Thermal resistance (R) or thermal conductivity (K), may be obtained from manufacturer of the material. Factors are related by the formula K = 1/R. (Fig. 23)
T = given thickness
R = thermal resistance for a given thickness (T) K = thermal conductivity
Noncombustible material with a lower R value may be used, provided thickness of material is sufficiently greater to maintain an equivalent (total) thermal resis- tance (Rt).
Example of Determining Hearth Extension
COMMON MATERIALS AND FACTORS
MATERIAL | K* | R | MINIMUM |
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THICKNESS |
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EH2416 | 0.916 | 2.18 | 1.0 in.** |
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(CFM Corporation) |
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Common Brick | 5.0 | 0.10 | 5.46 in.** |
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R Value is for 1/2 inch. |
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* Units of K = BTU/SQ FT/HR/˚F/IN |
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** Thickness of Listed Material |
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Fig. 23 Hearth extension material factors.
Equivalents
To determine the thickness required for any new mate- rial:
Example for Common Brick
NEW | K of new material (per inch) | thickness | |
required = |
| X | of listed |
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thickness | K of listed material (per inch) | material | |
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required thickness).
Wall Covering | 2 x 4 Header - Do not | |
notch at standoffs | ||
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Noncombus- |
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tible Decorative |
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Facing |
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Seal all cracks | NOTE: No | |
between fireplace sur- | material | |
round (steel) and wall | may cover | |
materials with noncom- | black cast | |
bustible material. | face. | |
Cast Front |
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Noncombustible |
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Decorative Cover- |
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ing |
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FP1202 | Safety Strips - Must be | |
overlapped 1/2” minimum |
Fig. 24 Sealing gaps.
16 | 20005167 |