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8 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 -8.4.
High temperature
(300°F min.) continuous,
non-combustible sealant
HX3 or HX4
Hearth Ext
Tile, stone or other
or equivilent
non-combustible material
insulation
(see Table below)
Floor constructed of wood or
other combustible material
Figure 8.1
Hearth Extension Construction
WARNING
Fire Risk
•
Metal hearth strips MUST be installed.
Sparks or embers may ignite ooring.
This replace has been tested and approved for use with a
hearth extension insulated to a minimum R value of 1.16.
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
•
Required thickness = Rk
•
Thermal resistance per inch thickness = r
2
•
r = (foot
)(hour)(°F) / (BTU)(inch)
•
Required thickness = R / rB.
Table 8.1
Hearth Extension Insulation Alternatives, R Value = 1.16
Material
Hearth & Home HX3, HX4
USG Micore 300™
USG Durock™ Cement Board
Cement Mortor
Common Brick
Ceramic Tile
Armstrong Privacy Plus
Marble
28
Protective
Metal Hearth
Strip
2 in. (51 mm)
required
2
)(hour)(°F)
k per inch
r per inch
thick
thick
0.43
2.33
0.46
2.18
1.92
0.52
5.0
0.20
5.0
0.20
12.50
0.08
14.3-20.0
0.07-0.05
Heat & Glo • EXCLAIM-42C • 4013-094 Rev I • 10/06
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)
Figure 8.2
Positioning the Protective Metal Hearth Strips
Minimum thickness
required
1/2 in.
1/2 in.
2-1/4 in.
5-7/8 in.
5-7/8 in.
14-5/8 in.
16-5/8 in. - 23-3/8 in.
WARNING
Fire Risk
•
Hearth extensions must be installed
exactly as speci ed.
High temperatures or hot embers may ignite
concealed combustibles.
1 in. overlap
.
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