Heatilator • LM42 • Installers Manual • 4087-901 • Rev A • 04/14/16
34
B. Hearth Extension, Construction and
Finishing
Table 7.1
R = 1/k x inches of thickness
Table 7.2
WARNING! Risk of Fire!
High temperatures, sparks,
embers or other burning material falling from the fire
-
place may ignite flooring or concealed combustible
surfaces.
• Protective metal hearth strips MUST be installed if
sitting on combustible surface.
• Hearth extensions are to be installed only as
illustrated to prevent high temperatures from
occurring on concealed combustible materials.
A hearth extension must be installed with all fireplaces
to protect the combustible floor in front of the fireplace
from both radiant heat and sparks.
• You MUST use a hearth extension with this
fireplace.
• Refer to Figure 7.2 for minimum dimensions.
• This fireplace has been tested and approved for use
with a hearth extension insulated to a minimum R
value of 1.03.
• The hearth extension material MUST be covered
with tile, stone or other non-combustible material.
• Manufactured hearth materials will usually have a
published
R value
(resistance to heat) or
k value
(conductivity of heat). Refer to the formula in Table
7.1 to convert a k value to an R value.
• The hearth extension construction may consist of
using one or more sources of material as long as
the R value is attained. See Table 7.2 and Figure
7.3.
• Refer to Table 7.2 for hearth extension insulation
alternatives.
NOTICE:
Hearth & Home Technologies is not
responsible for discoloration, cracking or other
material failures of finishing materials due to heat
exposure or smoke. Stainless steel will discolor
with temperature.
Figure 7.2 Hearth Extension Dimensions
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.
Armstrong™ Privacy Guard
Plus
0.46
2.18
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.
Marble
14.3-20.0
0.07-0.05
14-5/8 in. - 20-3/8
in.
Hearth Extension Dimensions
Model #
A
B
C
LM42
in.
58
16
8
mm
1473
406
203
A
C
C
B
To Reduce the Risk of Sheetrock Cracking
Finish With:
All purpose joint
compound.
Eggshell paint
(gloss or semi-gloss).
Facing Material
• Facing and/or finishing materials must never overhang
into the glass opening.
• Observe all clearances when applying combustible
materials.
Painting
If desired finishing includes a painted wall, 100% acrylic
latex with compatible primer is recommended around this
appliance. Oil-based or standard acrylic paints may dis
-
color due to heat exposure.
