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17
Majestic Fireplaces® BR/BC Series
7412944
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 = --------------------------------------- X 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).
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
Common Brick
0.458
5.0
1.09 0.50 in.**
0.10 5.46 in.**
(CFM Corporation)
R Value is for 1/2 inch.
* Units of K = BTU/SQ FT/HR/˚F/IN
** Thickness of Listed Material
FP533ADD
Addendum
6/1/99 djt
8/4/99 changed .2 to .1
one inch to 1/2 inch djt
FP533ADD
Fig. 24 Hearth extension material factors.
FP550
Fig. 25 Sealing gaps.
FP550
BR/BC - SEALING
DETAILS
9/29/97
Wall Covering
Noncombustible
Decorative
Facing
Noncombustible
Decorative
Covering
Seal all cracks
between fireplace
surround and wall
materials with
noncombustible
material.
Seal crack
between fireplace
and hearth extension
with noncombustible
material.
2x
4" HEADER -
Do not notch at
standoffs.
Safety Strips -
Must be overlapped
¹⁄₂
" minimum.
Hearth
Extension
Insulation
Side View