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112435-01M 7
HEARTH ExTENSION
A hearth extension projecting a minimum of 20"
in front of and a minimum of 12" beyond each
side of the replace opening is required to protect
combustible oor construction in front of the re-
place. Fabricate a hearth extension using a material
which meets the following specications: a layer
of noncombustible, inorganic material having a
thermal conductivity 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 ber,
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 extension
is to be covered, use noncombustible material such
as tile, slate, brick, concrete, metal, glass, marble,
stone, etc. Provide a means to prevent the hearth
extension from shifting and seal gap between the
replace frame and hearth extension with a non-
combustible material (see Figure 3).
is to be installed only as shown
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
A mantel may be installed if desired (see Figure 4).
Woodwork such as wood trims, mantels or any oth-
er combustible material projecting from the front
face must not be placed within 12" (GM36) or 18"
(GM42/50) of the replace opening. Combustible
materials above 12" (GM36) or 18" (GM42/50)
and projecting more than 1
1
/
2
" from the replace
must not be placed less than 15" (GM36) or 21"
(GM42/50) from the top opening of the replace
(NFPA STD 211, Sec. 7-3.3.3).
Mantels or any other combustible material also
may come up to the side edge of the black metal
face of the replace just as long as the projection
from the front face fall within the limit shown in
Figure 4.
12
1
/
4
" Ref.
15" Min.
(GM36)
21" Min.
(GM42/50)
12" Min. (GM36)
18" Min. (GM42/50)
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" - GM36
18" - GM42/50
7.75" (GM36)
11.5" (GM42/50)
33°
Combustible
Material Must
Not Overlap
Front Face
6"
Ref.