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(THERMAL CONDUCTIVITY) "K" = BTU in./hr. ft
2
°F
TO SUBSTITUTE ALTERNATE INSULATION MATERIAL, YOU NEED TO KNOW THE "K"
FACTOR FOR THAT MATERIAL. TO CALCULATE THE REQUIRED THICKNESS FOR THE
ALTERNATE MATERIAL USE THE FOLLOWING FORMULA:
K ALT.
.43
EXAMPLE:“K” OF BRICK = 5
5
.43
A hearth extension must be installed with all fire-
places. It is to protect the combustible floor in front of
the fireplace from both radiant heat and sparks.
The construction of and materials used for a factory-
built hearth extension are shown in Figure 5.
A hearth extension of this construction may be cov-
ered with any non-combustible decorative material
and may have a maximum thickness of 6" for the
BW36 and 3” for the BW36C. Seal gaps between the
hearth extension and the front of the fireplace with a
non-combustible sealant.
3. HEARTH EXTENSIONS.
4-00 10 30491D
Figure 5
Factory-Built Hearth Extension
Figure 6
Hearth Extension
EXAMPLES OF INSULATION
USG MICORE CV230 1/2" 0.43
REQUIRED
THICKNESS
K VALUE
x .5 = THICKNESS OF ALTERNATE MAT. (INCHES)
x .5 = 5.81 IN. OF BRICK.
BW36 SERIES WOODBURNING FIREPLACE
NON-COMBUSTIBLE
DECORATIVE MATERIAL
HX3 FACTORY-BUILT
HEARTH EXTENSION
HEARTH SEALING STRIP
GAP (SEAL WITH NON-COMBUSTIBLE SEALANT)
BLACK FIREPLACE BOTTOM
BW36-6"
BW36C-3"
1
/2"
52"
16"
NON-COMBUSTIBLE DECORATIVE
COVERING OR .018 MIN. SHEET METAL
INSULATION MIN. R VALUE 1.16
WARNING!
HEARTH EXTENSIONS ARE TO BE INSTALLED ONLY AS ILLUSTRATED
TO PREVENT HIGH TEMPERATURES FROM OCCURRING ON CON-
CEALED COMBUSTIBLE MATERIALS. HEARTH SEALING STRIPS PRE-
VENT BURNING OR HOT PARTICLES FROM INADVERTENTLY FALLING
DIRECTLY ON COMBUSTIBLE SURFACES IN THE EVENT THE BUILDING
SHOULD SETTLE AND DISTURB THE ORIGINAL CONSTRUCTION.
No one builds a better fire
Field constructed Hearth Extensions should be constructed in accordance with
the minimum dimensions provided in Figure 6.