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122272-01C 5
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 floor construction
in front of the replace. Fabricate a hearth
extension using a material which meets the
following specications: a layer of noncom-
bustible, 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 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 the hearth extension from
shifting and seal gap between the replace
frame and hearth extension with a noncom-
bustible material (see Figure 3).
is to be installed only as shown
in Figure 3.
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 replace opening.
Combustible materials above 12" and pro-
jecting more than 1
1
/
2
" from the replace
must not be placed less than 15" 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.
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
6"
Ref.
OPTIONAL OUTSIDE AIR KIT
Installation of an outside air kit should be per-
formed during rough framing of replace due
to nature of it's location. Outside combustion
air is accessed through a vented crawl space
(AK4F) or through a sidewall (AK4). This re-
place is equipped with a barometric damper
which allow outside air to ow into replace
automatically when needed.