Majestic BR36 Operating Manual page 17

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
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 conductiv-
ity (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
EH2416
0.458
(CFM Corporation)
Common Brick
5.0
R Value is for ¹⁄₂ inch.
* Units of K = BTU/SQ FT/HR/ßF/IN
** Thickness of Listed Material
Fig. 24 Hearth extension material factors.
7412944
MINIMUM
R
K*
THICKNESS
1.09 0.50 in.**
0.10 5.46 in.**
FP533ADD
Majestic Fireplaces
Wall Covering
Noncombustible
Decorative
Facing
Seal all cracks
between fireplace
surround and wall
materials with
noncombustible
material.
Noncombustible
Decorative
Covering
Hearth
Extension
Insulation
Side View
Fig. 25 Sealing gaps.
Example of Determining Hearth Extension
Equivalents
To determine the thickness required for any new
material:
NEW
K of new material (per inch)
required =
thickness
K of listed material (per inch)
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required
thickness).
BR/BC Series
®
2 x 4" HEADER -
Do not notch at
standoffs.
Seal crack
between fireplace
and hearth extension
with noncombustible
material.
Safety Strips -
Must be overlapped
¹⁄₂" minimum.
FP550
thickness
x
of listed
material
17