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Outdoor Lifestyles by Hearth & Home Technologies Inc. • Montana US-CAN • 4039-156 Rev K • 7/11
23
8
Finishing
A. Hearth Extension
A hearth extension must be installed with all replaces to
protect the combustible oor in front of the replace from
both radiant heat and sparks. See Figures 8.1 -8.3.
2 in. (51 mm)
required
Continuous,
non-combustible sealant
Tile, stone or other
non-combustible material
Floor constructed of wood or
other combustible material
1/2 in. Micore
Hearth Ext
or equivalent
insulation
(see Table 11.2)
Fireplace
Protective
Metal Hearth
Strip
Figure 8.1 Hearth Extension Construction
Protective metal strips are placed 2 in. (51 mm) under the
front of the fireplace and must extend beyond the front
and sides of fireplace opening by 2 in. (51 mm).
1 in. (25 mm)
overlap
Figure 8.2 Positioning the Protective Metal Hearth Strips
The hearth extension should slope away from the front of the
replace and chase at 1/8 in. to 1/4 in. per foot. Spark strips
must be used on top of any combustible hearth materials
used for moisture management.
This replace has been tested and approved for use with a
hearth extension insulated to a minimum R value of 1.03.
To substitute materials for the factory-available hearth ex-
tensions, see Figure 8.3 and calculate insulation alterna-
tives as per Table 8.1 and the following formulas:
• Thermal conductivity per inch thickness = k
• k = (BTU)(inch) / (foot
2
)(hour)(°F)
• Required thickness = Rk
• Thermal resistance per inch thickness = r
• r = (foot
2
)(hour)(°F) / (BTU)(inch)
• Required thickness = R / rB.
A
B
C
Figure 8.3 Hearth Extension Dimensions
Fire Risk
• Metal hearth strips MUST be installed.
Sparks or embers may ignite ooring.
WARNING
Fire Risk
• Hearth extensions must be installed
exactly as specied.
High temperatures or hot embers may ignite
concealed combustibles.
WARNING
Table 8.1
CAT. # A B C
HX3 in 52 16 8
mm 1321 406 203
HX4 in 66 20 12
mm 1676 508 305
Hearth Extension Insulation Alternatives-Total minimum R Value must equal 1.03
Material
k per inch
thick
r per inch
thick
Minimum
thickness
required
Hearth & Home HX3, HX4 (Micore 300™) 0.49 2.06 1/2 in.
USG Micore 160™ 0.39 2.54 1/2 in.
USG Durock™ Cement Board 1.92 0.52 2 in.
Cement Mortor 5.0 0.20 5-1/8 in.
Common Brick 5.0 0.20 5-1/8 in.
Ceramic Tile 12.50 0.08 12-1/4 in.
Armstrong™ Privacy Guard Plus 0.46 2.18 1/2 in.
Marble 14.3-20.0 0.07-0.05 14-5/8 in. - 20-3/8 in.