Finishing; Hearth Extension - Heatilator A36R Owner's Manual

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.
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 1.03.
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
• Required thickness = Rk
• Thermal resistance per inch thickness = r
• r = (foot 2 )(hour)(°F) / (BTU)(inch)
• Required thickness = R / rB.
Table 8.1
Hearth Extension Insulation Alternatives-Total minimum R Value must equal 1.03
Material
Hearth & Home HX3, HX4 (Micore 300™)
USG Micore 160™
USG Durock™ Cement Board
Cement Mortor
Common Brick
Ceramic Tile
Armstrong™ Privacy Guard Plus
Marble
2 )(hour)(°F)
k per inch
thick
0.49
0.39
1.92
5.0
5.0
12.50
0.46
14.3-20.0
Heatilator • A36R & A42R • 28376 Rev AC • 11/07
HX3 or HX4
Hearth Ext
or equivalent
insulation
(see Table below)
Floor constructed of wood or
other combustible material
Figure 8.1 Hearth Extension Construction
Minimum
r per inch thickness
thick required
2.06 1/2 in.
2.54 1/2 in.
0.52 2 in.
0.20 5-1/8 in.
0.20 5-1/8 in.
0.08 12-1/4 in.
2.18 1/2 in.
0.07-0.05 14-5/8 in. - 20-3/8 in.
High temperature
(300°F min.) continuous,
non-combustible sealant
Tile, stone or other
non-combustible material
2 in. (51 mm)
required
Protective
Metal Hearth
Strip
27