Installation manual
HEARTH
EXTENSION:
EXAMPLE
OF
DETERMING
HEARTH
EXTENSION
EQUIVALENT
If
there
is a
combustible
floor construction
in
front
of
the
fireplace,
a
heaRh
extension
is required
to
prolect
it.
The
hearth
extension,
as
shown
in
Figure
35,must
be
a
minimum
of
20"
deep
by
65"
wide
and
extend
a
minimum
of
12"
beyond each
side
of
the
fireplace opening.
FIGURE
35
The
hearth extension must
be
made from
a
non-com-
bustible inorganic material with
a
thermal conductivity,
K
of
.27
or less. The thermal conductivity,
K
or thermal
resistance.
R
of
materials can usually be obtained from
the manulacturer.
The
factors are related
by
the for-
mula
K
=
-,!,
The
thickness required for various common
materials and their factors are shown
in
Figure
36.
FIGURE
36
-
COMMON
MATERIALS
AND THEIR
FACTORS
To
determine
the
thickness
required
for
any
material:
K
new
material
x
1"
=
Thickness
Required
.84
Example
for
Insulating
Board-K-FAG
19
(K
trom
Figure
36).
Whatever the material used, sufficient thickness
must
be
laid down to maintain an equivalent
K
factor.
The thermal insulating layer may be covered by any
non-combustible material such
as
metal,
tile,
slate,
brick, glass, concrete, marble, or stone. When using
a
low density insulating material a supporting
metat
cover
such
as
shown
in
Figure
37
should
be
fabricated
and
installed.
NOTE:
Some
non-combustible coverings
such
as
metal,
slate,
sandstone and marble
are
rela-
tively
gcad
conductors
of
heat and rnusl
be
used in
combination with the more thermally resistant materi-
als.
In finishing
up
the hearlh extension,
be
sure to fasten
it
securely to
the
floor
to
prevent shifting, and seal the
gap
between
the
fireplace frame and the hearlh
extension
with
a
non-combustible material (see
Figures
38
&
39).
METAL
COVER
DESIGN CONSlSTS
OF
A
TOP
AND
4
SIDES
AS
REQUIRED
BY
DESIGN
NOTCH CORNERS
THEN
BEND FLANGES
$0'.
65" MIN.
MATERIAL
318
MIN.
THlCKNESS
GALVANIZE0
2O"MIN.
OR
ALUMINUM
STEEL
FIGURE
37-
METAL
COVER
CONSTRUCTION
NON-COMBUSTIBLE DECORATIVE
COVERING:
Should
be
at
least
3/8"
thick and meet Iccal building
code requirements. The finished height of
the
hearth
extension must not block the inlet grille at the bottom
of
the fireplace.