THE CAUTIONS BELOW RELATE TO LOCATIONS ON
FIGURE 4.
A. The hearth safety strip must be used under the crack
between the fireplace and the hearth extension when the
fireplace is installed on a combustible floor. Seal the
crack with a non-combustible material such as mortar,
grout, etc.
B. COMBUSTIBLE MATERIALS MUST NOT OVERLAP
THE SURFACE OF THE BLACK FRONT FACE
PANELS. COMBUSTIBLES MAY BE INSTALLED
OVER THE SIDE NAIL FLANGES UP TO THE EDGE
OF THE FRONT FACE SURFACE.
?
DO NOT BLOCK HEAT CIRCULATING AIR INLETS
OR OUTLETS. DOING SO MAY RESULT IN A
POTENTIAL FIRE HAZARD.
C. If the floor in front of the fireplace is combustible, either a
raised or floor-level protective hearth extension must be
constructed. For TFC39 only, a raised hearth extension
may be flush with the fireplace hearth. To construct a
raised hearth extension with louvered models, the
fireplace must rest on a raised platform. A raised hearth
extension must be a minimum of 16" x 52" and be
constructed of materials with an R-factor equal to or
greater than 1.20. A hearth extension installed directly on
the floor must be a minimum of 16" x 52" and be
constructed of materials with an R-factor equal to or
greater than .80. If combustible materials are used to
construct the hearth extension, they must not touch the
black surface of the fireplace. The same material that is
used to protect the top of the hearth extension must be
placed between the combustible and the black face of
the fireplace. The hearth extension must be fastened to
the floor to prevent shifting and the gap between the
fireplace and the hearth extension must be sealed with a
noncombustible material if a metal safety strip is not
used. These materials (listed below) may be used for a
wall shield as well.
D. The framing header may rest on top of the standoffs.
E. The minimum distance from the fireplace opening to an
adjacent combustible wall is 17½". The minimum
distance to an adjacent combustible wall may be reduced
to 12" when an approved wall shield is used on the wall.
The wall shield must be 40" x 40" and be constructed of
a noncombustible, inorganic material having a thermal
resistance of R = 1.49.
Determining the R-Values
The hearth extension must be constructed of non-
combustible materials which have a total thermal resistance
(R factor) equal to or greater than .80 for floor level hearth
extensions or 1.20 for raised hearth extensions and be a
minimum size of 16" x 52". Choose the desired materials
and obtain the K value at 75° mean temperature. The C
value and the R value may be calculated with the following
formulas:
K = Thermal conductivity. K = BTUs-ins./hrs.-ft.
2
-
0
F
T = thickness C= Thermal conductance
R = Thermal resistance K/T = C; 1/C = R
Example
: 3/4" Marble with 3/8" Micore
Determine the R value for each material used as follows:
Marble:K/T= 11/.75=14.66.
1/C = 1/14.66 = 0.068 (R factor)
Micore 300: K/T = .458/.375 = 1.22.
1/C = 1/1.22=0.82 (R factor)
After the R value is obtained on each material in this hearth,
add the R values to obtain total thermal resistance (R).
Total R factor = 0.068 + 0.82=0.89
The total must be equal to or greater than specified above.
Typical materials: Micore 300 has a K of .458; Micore 230
has a K of .43; Micore 180 has a K of .34; Ceraboard has a
K of .34; common brick has a K of 5; cemen t mortar has a K
of 5; marble has a K of 11; limestone has a K of 6.5; tile has
a K of 12; slate has a K of 21; Wonder Board has a K value
of 3.2.
MICORE NC 180-300, manufactured by U.S. GYPSUM
CORPORATION
CONWED SPEC 300, manufactured by CONWED
CORPORATION
CERA FORM TYPE 106R board, manufactured by
JOHNS-MANVlLLE.
WONDER BOARD, manufactured by GOLD BOND
BUILDING PRODUCTS.
6
Framing Members
Framing Members
Figure 4
