424WBST Designer Woodburning Fireplaces
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 | = |
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| X of listed |
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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).
COMMON MATERIALS AND FACTORS
MATERIAL | K* | R | MINIMUM | |
THICKNESS | ||||
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EH2416 | 0.458 1.09 | 0.50 in.** |
(MHSC) |
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Common Brick 5.0 0.10 | 5.46 in.** | |
R Value is for 1/2 inch.
*Units of K = BTU/SQ FT/HR/˚F/IN ** Thickness of Listed Material
Fig. 25 Hearth extension material factors. | FP533AD | |
| 2x4" |
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Wall Covering | Stud |
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Noncombustible | 5/O" |
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Decorative |
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Facing | 5/O" |
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Seal all cracks | Outer Dome | NOTE: 5/O" |
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between fireplace |
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surround and wall |
| air space |
materials with | 2x4" Header - | between |
noncombustible | Outer Dome | |
material. | Do not notch at | and |
| standoffs. | combustible |
Noncombustible |
| materials |
Decorative |
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Covering |
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| Seal crack |
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Hearth Extension | between fireplace | |
Insulation | and hearth extension | |
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| material. |
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Side View |
| Safety Strips - |
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| Must be overlapped |
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| 56O" minimum. |
FP719
Fig. 26 Finish wall treatments and gap sealing.
Seal Cracks Between Fireplace and Hearth |
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Extension with Noncombustible Material |
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Noncombustible | Lower Surround |
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Material 7Z\x" |
| Noncombustible |
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Max. Thickness | Fireplace | |||
Material | ||||
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Combustible | Hearth | |||
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Floor |
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1/4" Min. Thickness | Safety Strips | |||
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| Must be Over- | |
| Minimum Insulation | lapped 1/2" Min. | ||
FP1170 | Value |
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Fig. 27 Hearth extension dimensions.
Recessed Installation - STR33/36 Only
Noncombustible |
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Material | Minimum |
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(if desired) |
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36” (914 mm) | A |
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Insulation |
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with Minimum | 6” |
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R Value |
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(152 mm) | Minimum | |||
of 2.75 | ||||
Minimum | ||||
| 33” | |||
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| (838 mm) | |
| 2” |
| 2” | |
| (51 mm) |
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| Hearth Extension |
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Minimum .030 Thick Stain- less Steel Plate
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| Insulation with Minimum R | |||||||
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| Value of 2.75 | |||||||
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| Minimum .030 | |||||||
Maximum |
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| Thick Stainless | |||||||||
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10” |
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| Steel Plate | |||||||||
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(254 mm) |
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Maximum
14” 
(356 mm)
Hearth | FP1608 |
Extension |
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View A
NOTE: If noncombustible material is not used between the stainless steel plate and fireplace opening, the steel must be attached to the front of the unit a minimum of four (4) places on each piece with sheet metal screws no longer than 1/2".
NOTE: The size of the insulation and stainless steel plate must be within limits stated above and covers all combustible framing material.
Fig. 28 Recessed installation.
18 | 87D1506 |