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All fireplaces installed over a combustible floor must incorporate a non-combustible hearth extension. It is
required to protect the floor in front of the fireplace from both radiant heat and sparks.
Hearth extension dimensions should be determined by using the chart below. use hearth extensions as illus-
trated in figures 6, 10 and 11 or use an acceptable thickness of a durable non-combustible material with an
equal or greater insulating value than K = .43 Btu in/ft
2
-HR-Fº, or a thermal resistance that equals or exceeds
R = 1.16. These materials should be covered with a decorative non-combustible veneer.
NOTE: Any non-combustible material with a K factor value that is less than .43, or whose R value is more than
1.16 for 1/2” thick material is acceptable.
HOW TO DETERMINE HEARTH EXTENSION REQUIREMENTS
The following information is provided to determine required thickness for any non-combustible material when
either the K or R values are known. They are expressed as the following: K = Btu-in/ft
2
-HR-Fº or R = HR-fº/Btu.
These materials should be covered by a decorative non-combustible material such as tile, brick, stone or slate.
To determine the thickness needed for a material other than those listed in the chart, use the following formulas
to calculate that which will be an acceptable equivalent.
The ability of insulating material to retard the transfer of heat may be expressed as either Thermal Conduc-
tance (C), Thermal Conductivity (K), or Thermal Resistance (R). The mathematical relationship of these
values and the formulas for converting one value to another is as follows:
C = K divided by the material thickness
(Example C = .43 divided by 1/2 (.50)
C = .86)
K = C multiplies by the material thickness
(Example K = .86 multiplied by 1/2 (.50)
K = .43)
R = The material thickness divided by K
(Example R = 1/2 (.50) divided by .43
R = 1.16)
With either type hearth extension minor shifting of the supporting floor or expansion and contraction may
eventually cause a crack to develop between the hearth extension and the face of the fireplace. To help
prevent the crack from developing, the hearth extension materials must be firmly fastened in place. Wall ties
should be screwed to the face of the fireplace and imbedded in the mortar joints of brick, stone, or other non-
combustible materials. The metal safety strip packed with the fireplace must be placed beneath the fireplace
and extended under the hearth extension or into a mortar joint of the hearth extension. In the event a crack
does eventually develop, the metal safety strip will serve as a barrier to prevent sparks or embers from falling
from the fireplace onto combustible flooring materials.
* See figure 6A for an alternate hearth extension using brick only.
WARNING: THE CRACK BETWEEN THE HEARTH EXTENSION AND FIREPLACE MUST BE SEALED WITH
A NON-COMBUSTIBLE MATERIAL. WHEN INSTALLING THE HEARTH EXTENSION, BE CAREFUL NOT
TO BLOCK THE HEAT CIRCULATING AIR INLETS (LOUVERS, SLOTS, ETC.). SEE FIGURE 6A.
Wall Protection
A model WS wall shield or an equivalent must be installed when the closed end of the fireplace is closer than
24 inches from a wall perpendicular to the face of the fireplace. (see figures 10 and 11). The WS wall shield
should be attached securely to the wall by driving nails or screws through it into the wall studs. The wall shield
should be covered by a decorative non-combustible material such as brick, tile, slate, etc.
The WS wall shield is constructed by 1 inch of Micore CV230 insulation board, manufactured by U.S. Gypsum
Corporation, covered by a sheet of galvanized metal. An alternate insulating material with a K factor of .43 or
lower can be used. refer to the preceeding section for instructions for selecting an alternate insulating material.
WARNING: IF NOT INSTALLED, OPERATED AND MAINTAINED IN ACCORDANCE WITH THE
MANUFACTURER’S INSTRUCTIONS, THIS PRODUCT COULD EXPOSE YOU TO SUBSTANCES IN FUEL
OR FROM FUEL COMBUSTION WHICH CAN CAUSE DEATH OR SERIOUS ILLNESS AND WHICH ARE
KNOWN TO THE STATE OF CALIFORNIA TO CAUSE CANCER, BIRTH DEFECTS OR OTHER REPRO-
DUCTIVE HARM. ALSO, OPERATION, INSTALLATION AND SERVICING OF THIS PRODUCT COULD EX-
POSE YOU TO AIRBORN PARTICLES OF GLASS WOOL FIBERS KNOW TO THE STATE OF CALIFORNIA
TO CAUSE CANCER THROUGH INHALATION.
FLOOR PROTECTION
53D9041. Rev 1 03/03