WARNING: Hearth extension must be installed in accordance with Figure 23 and must not cover the bottom front opening of the circulating model.
Alternate noncombustible materials may be used pro- viding the (total) thermal resistance (Rt value) of the al- ternate 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. 24)
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).
COMMON MATERIALS AND FACTORS
MATERIAL | K* | R | MINIMUM | |
THICKNESS | ||||
EH2416 | 0.458 | 1.09 | 0.50 in.** | |
(MHSC) | ||||
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Common Brick | 5.0 | 0.10 | 5.46 in.** | |
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R Value is for 1/2 inch.
*Units of K = BTU/SQ FT/HR/˚F/IN ** Thickness of Listed Material
FP533ADD
Fig. 22 Hearth extension material factors.
Example of Determining Hearth Extension Equivalents
To determine the thickness required for any new mate- rial:
NEW |
| K of new material (per inch) | thickness |
required | = | of listed | |
thickness |
| K of listed material (per inch) | material |
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required thickness).
M400BFC Balanced Flue
Wall Covering | Side View |
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Noncombustible | 2 x 4” Header |
Decorative Fac- | - Do not notch at |
ing | standoffs |
Seal all cracks between fireplace surround and wall materials with non- combustible material.
Noncombus- tible Decorative Covering
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| Seal crack between |
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Hearth Exten- |
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| fireplace and hearth | |
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| extension with noncom- | ||
sion Insulation |
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| bustible material | |
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| Safety Strips - |
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| Must be overlapped 1/2” |
FP550 |
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Fig. 23 Sealing gaps.
Glass Door Operation
The M400BFC is intended for use only with the doors fully closed. (Fig. 28)
| Correct | Wrong |
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| KT108b |
Fig. 28 | Correct door position. |
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87D1505 | 17 |
