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Heatilator • Birmingham BIR50-B Installation Manual • 4059-701 • Rev G • 06/29/15
B. Hearth Extension, Building and Finishing
Table 6.1
R = 1/k x inches of thickness
Table 6.2
WARNING! Risk of Fire!
High temperatures, sparks, em-
bers or other burning material falling from the fireplace
may ignite flooring or concealed combustible surfaces.
• Protective metal hearth strips MUST be installed.
• Hearth extensions MUST be installed exactly as
specified.
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 6.4 for minimum dimensions.
• This fireplace has been tested and approved for use with
a hearth extension insulated to a minimum R value of
2.06.
• 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 6.1
to convert a k value to an R value,
• Refer to Table 6.2 for hearth extension insulation
alternatives.
74 in.
(1880 mm)
50 in.
(1270 mm)
12 in.
(305 mm)
12 in.
(305 mm)
20 in. (508 mm) Minimum
Figure 6.4 Standard Hearth Extension Dimensions
* 2 in. (51 mm)
Continuous,
non-combustible sealant
Tile, stone or other
non-combustible material
Floor constructed of wood or
other combustible material
1 in. Micore and 1/2
in. Durock or
equivalent insulation
(see Table)
Fireplace
Protective
Metal Hearth
Strip
Durock
*
*
Note:
The bottom of the fireplace opening is 3-3/4 in. (95.3mm) above
the bottom of the fireplace. Finished hearth must NOT extend above this
level.
Figure 6.5 Standard Hearth Extension Construction
1. Fireplace Installed Flush on the Floor and
Hearth Extension Raised to Bottom of Firebox
Opening
Non-combustible flooring a minimum of 20 in. (508 mm)
in front of and 12 in. (305 mm) to each side of the fuel
opening is required.
The hearth framing must be constructed of non-com-
bustible materials (such as metal framing or equivalent
material) and placed on HX3(s) or HX4(s) and 1/2 in.
Durock, or equivalent material. See Figures 6.4 and 6.5.
When creating the platform, allow for the thickness
of the non-combustible finishing materials
.
Seal gaps between the hearth extension and the front
of the fireplace with a bead of non-combustible sealant
or grout.
Hearth Extension Insulation Alternatives, R Value = 2.06
Material
k per inch
thick
r per inch
thick
Minimum
thickness
required
Hearth & Home HX3, HX4
0.49
2.06
1 in.
USG Micore 300™
0.49
2.06
1 in.
USG Durock™ Cement Board
1.92
0.52
4 in.
Cement Mortar
5.0
0.20
10 1/2 in.
Common Brick
5.0
0.20
10 1/2 in.
Ceramic Tile
12.50
0.08
25 3/4in.
Armstrong™ Privacy Guard Plus
0.46
2.18
1 in.
Marble
14.3-20.0
0.07-0.05
29 1/2 - 41 1/4 in.
