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116010-01E
5
HEARTH ExTENSION
A hearth extension projecting a minimum of
20" in front of and a minimum of 12" beyond
each side of fireplace opening is required to
protect combustible floor construction in front
of fireplace. Fabricate a hearth extension
using a material which meets the following
specifications: a layer of noncombustible,
inorganic material having a thermal conduc
-
tivity of K=0.84 BTU IN/FT, HR. F (or less) at
1" thick. For example, if the material selected
has a K factor of 0.25, such as glass fiber, the
following formula would apply:
0.25
x 1.0" = 0.30" thickness required
0.84
Thermal conductivity "K" of materials can be
obtained from the manufacturer or supplier of
the noncombustible material. If the hearth ex
-
tension is to be covered, use noncombustible
material such as tile, slate, brick, concrete,
metal, glass, marble, stone, etc. Provide
a means to prevent hearth extension from
shifting and seal gap between fireplace frame
and hearth extension with a noncombustible
material (see Figure 3).
WARNING: Hearth extension
is to be installed only as shown
in Figure 3.
Fireplace insTallaTion
Continued
Figure 3 - Hearth Extension
Seal Gap
Fireplace Front
Ember Protector
Fireplace Front
Raised Hearth
Fireplace Front
Elevated
Ember Protector
Ember Protector
Seal Gap
Hearth
Extension
MANTELS
A mantel may be installed if desired (see Figure
4). Woodwork such as wood trims, mantels or
any other combustible material projecting from
the front face must not be placed within 12" of
the fireplace opening. Combustible materials
above 12" and projecting more than 1
1
/
2
" from
the fireplace must not be placed less than 15"
from top opening of fireplace (NFPA STD 211,
Sec. 7-3.3.3).
Mantels or any other combustible mate
-
rial also may come up to side edge of black
metal face of fireplace as long as projection
from front face fall within the limit shown in
Figure 4.
12
1
/
4
" Ref.
15" Min.
12" Min.
1
1
/
2
" Max.
3" Nom.
33°
Combustible
Material
Safe
Zone for
Projection of
Combustible
Materials
Fireplace
Opening
Upper
Section of
Fireplace
Figure 4 - Mantel Clearances to
Combustible Material
FIREBOX
SAFE ZONE
Top View of Fireplace
3" Max.
4.5"
Min. to
Perpendicular
Side Wall
12"
7.75"
33°
Combustible
Material Must
Not Overlap
Front Face
6"
Ref.
