A hearth extension must be installed with all fire-
places. It is to protect the combustible floor in front of
the fireplace from both radiant heat and sparks.
The construction of and materials used for a field con-
structed hearth extension are shown in Figure 5.
A hearth extension of this construction may be cov-
ered with any non-combustible decorative material
and may have a maximum thickness of 7
1
⁄
2
". Seal
gaps between the hearth extension and the front of
the fireplace with a non-combustible sealant.
2. HEARTH EXTENSIONS
3-00
10 33147A
Figure 5
Field Constructed Hearth Extension
Figure 6
Hearth Extension
(THERMAL CONDUCTIVITY) "K" = BTU in./hr. ft
2
°F
TO SUBSTITUTE ALTERNATE INSULATION MATERIAL, YOU NEED TO KNOW THE "K"
FACTOR FOR THAT MATERIAL. TO CALCULATE THE REQUIRED THICKNESS FOR THE
ALTERNATE MATERIAL USE THE FOLLOWING FORMULA:
K ALT.
.43
EXAMPLES OF INSULATION
USG MICORE CV230
1/2"
0.43
MINIMUM
REQUIRED
THICKNESS
K VALUE
x .5 = THICKNESS OF ALTERNATE MAT. (INCHES)
EXAMPLE:“K” OF BRICK = 5
5
.43
x .5 = 5.81 IN. OF BRICK.
WARNING!
HEARTH EXTENSIONS ARE TO BE INSTALLED ONLY AS ILLUSTRATED TO
PREVENT HIGH TEMPERATURES FROM OCCURRING ON CONCEALED COM-
BUSTIBLE MATERIALS. HEARTH SEALING STRIPS PREVENT BURNING OR
HOT PARTICLES FROM INADVERTENTLY FALLING DIRECTLY ON COM-
BUSTIBLE SURFACES IN THE EVENT THE BUILDING SHOULD SETTLE AND
DISTURB THE ORIGINAL CONSTRUCTION.
RHW-44 WOODBURNING FIREPLACE
Field constructed Hearth Extensions should be constructed in accordance with Figures 5 and 6 instructions. In
all cases, the hearth extension must extend a minimum of 16” to the front and 8” on either side of the fireplace
opening. The field constructed hearth extension must be constructed from 1/2” MICORE CV230.