WARNING: HEARTH EXTENSION MUST BE IN- STALLED 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.** |
| |
(CFM Corporation) |
| ||||
|
|
|
|
|
|
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
| FP533ADD |
Fig. 24 Hearth extension material factors. | |
Wall Covering |
|
Noncombustible | 2x4" HEADER - |
Decorative | Do not notch at |
Facing | standoffs. |
Seal all cracks |
|
between fireplace |
|
surround and wall |
|
materials with |
|
noncombustible |
|
material. |
|
Noncombustible |
|
Decorative |
|
Covering |
|
Hearth | Seal crack |
Extension | between fireplace |
Insulation | and hearth extension |
| with noncombustible |
| material. |
Side View | Safety Strips - |
| Must be overlapped |
FP550 | ���" minimum. |
Fig. 25 Sealing gaps. |
|
Majestic Fireplaces® BR/BC Series
Example of Determining Hearth Extension Equiva- lents
To determine the thickness required for any new mate- rial:
NEW | K of new material (per inch) | thickness |
required = | X of | |
listed |
|
|
thickness | K of listed material (per inch) | mate- |
rial |
|
|
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required thickness).
Recessed Installation - BR/BC36 Only
Noncombustible |
|
|
|
Material | Minimum |
| |
(if desired) |
| ||
36” (914 mm) A |
| ||
|
| ||
Insulation |
|
|
|
with Minimum |
| 6” |
|
R Value |
|
| |
| (152 mm) | Minimum | |
of 2.75 |
| ||
| Minimum | ||
|
| 33” | |
|
|
| |
|
|
| (838 mm) |
| 2” | 2” |
|
| (51 mm) | (51 mm) |
|
| Hearth Extension |
| |
|
| A |
|
| Minimum .030 Thick Stain- |
| |
| less Steel Plate |
| |
|
| Insulation with Minimum R | |
|
| Value of 2.75 |
|
|
| Minimum .030 |
|
Maximum |
| Thick Stainless |
|
10” |
| Steel Plate |
|
(254 mm) |
|
|
|
Maximum
14” 
(356 mm)
Hearth | FP1608 |
Extension |
|
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. 26 Recessed installation.
7412944 | 17 |