FMI WCM-42G - Manual (Page 7)

www.fmiproducts.com 122271-01D 7
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 manufacturer or supplier of
noncombustible material. If hearth extension
is to be covered, use noncombustible mate-
rial 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 6).
WARNING: Hearth extension
is to be installed only as shown
in Figure 6.
Fireplace inSTallaTion
Continued
Figure 6 - 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
7). Woodwork such as wood trims, mantels or
any other combustible material projecting from
front face must not be placed within 12" (36"
Models) or 18" (42/50" Models) of fireplace
opening. Combustible materials above 12" (36"
Models) or 18" (42/50" Models) and projecting
more than 1 1 /
2
" from fireplace must not be
placed less than 15" (36" Models) or 21" (42/50"
Models) from the top opening of the fireplace
(NFPA STD 211, Sec. 7-3.3.3).
Mantels or any other combustible material
also may come up to side edge of black metal
face of fireplace as long as projections from
front face fall within limit shown in Figure 7.
12 1 /
4
" Ref.
6"
Ref.
15" Min. (3
6"
M
od
el
s)
21" Min. (4
2/
50
"
Models)
12" Min.
(36" Models)
18" Min. (42/50" Models)
1 1 /
2
" Max.
3" Nom.
33°
Combustible
Material
Safe
Zone for
Projection of
Combustible
Materials
Fireplace Opening
Upper
Section of
Fireplace
Figure 7 - Mantel Clearances to
Combustible Material
FIREBOX
SAFE ZONE
Top View of Fireplace
3" Max.
4.5"
Min. to
Perpendicular
Side Wall
7.75" (36" Models)
11.5" (42/50" Models)
33°
Combustible
Material Must
Not Overlap
Front Face
12" - 36" Models
18" - 42/50" Models