Heatilator CST42A, Owner'S Manual, Page: 25 / 48

Heatilator • CST42A • 4012-012 Rev J • 08/06
25
8 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.
2 in. (51 mm)
required
High temperature
(300°F min.) continuous,
non-combustible sealant
Tile, stone or other
non-combustible material
Floor constructed of wood or
other combustible material
HX3 or HX4
Hearth Ext
or equivilent
insulation
(see Table below)
Fireplace
Protective
Metal Hearth
Strip
Figure 8.1 Hearth Extension Construction
1 in. (25 mm) overlap
Metal strips are placed 2 in. (51 mm) under the front
of the fireplace and must extend beyond the front
and sides of fireplace openings by 2 in. (51 mm).
Figure 8.2 Positioning the Protective Metal Hearth Strips
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
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
fl ooring.
WARNING
Fire Risk
• Hearth extensions must be installed
exactly as speci fi ed.
High temperatures or hot embers may ignite
concealed combustibles.
WARNING
Table 8.1
Hearth Extension Insulation Alternatives, R Value = 1.16
Material
k per inch
thick
r per inch
thick
Minimum
thickness
required
Hearth & Home HX3, HX4 0.43 2.33 1/2 in.
USG Micore 300™ 0.46 2.18 1/2 in.
USG Durock™ Cement Board 1.92 0.52 2-1/4 in.
Cement Mortar 5.0 0.20 5-7/8 in.
Common Brick 5.0 0.20 5-7/8 in.
Ceramic Tile 12.50 0.08 14-5/8 in.
Armstrong™ Privacy Guard Plus .046 2.18 1/2 in.
Marble 14.3-20.0 0.07-0.05 16-5/8 in. - 23-3/8 in.
Model # A B C
HX4
in. 66 20 12
mm 1676 508 305