8
Finishing
A. Hearth Extension
A hearth extension must be installed with all fi replaces to
protect the combustible fl oor in front of the fi replace from
both radiant heat and sparks. See Figures 8.1 -8.3.
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 fl ooring.
This fi 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 alternatives
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 Mortar
Common Brick
Ceramic Tile
Armstrong™ Privacy Guard Plus
Marble
24
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
.046
2.18
14.3-20.0
0.07-0.05
16-5/8 in. - 23-3/8 in.
Heatilator • ST42A • 35038 Rev G • 02/05
Metal strips are placed 2 in. (51 mm) under the
front of the fireplace and must extend beyond the
front and sides of fireplace by 2 in. (51 mm).
Figure 8.2
Positioning the Protective Metal Hearth Strips
Fire Risk
•
High temperatures or hot embers may ignite
concealed combustibles.
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.
1/2 in.
1 in. (25 mm) overlap
WARNING
Hearth extensions must be installed
exactly as specifi ed.
A
C
Model #
A
in.
66
HX4
mm
1676
Figure 8.3
Hearth Extension Dimensions
B
B
C
20
12
508
305