8
The hearth and/or floor protection must be a thermally rated non-
combustible hearth/floor protector meeting or exceeding a thermal
rating of k=.84 or equivalent with a listed thickness of listed thickness
of 3/4" (19 mm) minimum in the USA and Canada. The covering must
extend USA-16”/Canada-18” (C260) in front of the heater and 8” to the
side (measured from door opening in the USA and measured from the
side of the unit in Canada).
Using Alternate Material As Floor / Hearth Protection
The hearth extension or alternate material used as a floor/hearth protec-
tor must be constructed of a durable noncombustible material having
an equal or better thermal conductivity value (lower k value) of k =.84
BTU/IN FT2 HR °F or a thermal resistance that equals or exceeds r = 1.19
HR °F FT2 IN/BTU with a minimum thickness of 3/4”. With these values,
determine the minimum thickness of the alternate material required using
the formula(s) and shown in
Table 2
.
NOTE:
Any noncombustible material having a minimum thickness of
3/4”(19 mm) whose k value is less than .84 or whose r value is more
than 1.19 is acceptable. If the alternate material used has a higher k value
or lower r value will require a greater thickness of the material used. In
some cases, if the k value is less or the r value higher, a thinner material
may be used.
Methods of determining floor protection equivalents:
To determine the thickness required for the alternate material when
either the
"k"
value or
"r"
value is known, use either the
k formula
or
r
formula
.
Example:
If Micore 160 Mineral Fiber Board is to be used for the floor
protection, how thick must this material be?
k
M
= k value per inch of
alternate
material
r
M
= r value per inch of
alternate
material
T
M
= minimum thickness required for
alternate
material
T
S
= standard thickness of the
alternate
material
k
L
= k value per inch of
listed
material
r
L
= r value per inch of
listed
material
T
L
= minimum thickness of
listed
material
NOTE:
An asterisk "
*
" indicates, it is a value taken from
Table 2
.
Using the k formula:
Minimum
k-value (per Inch) of
Specified min.
thickness of = alternate material (
k
M
) x
thickness
alternate
k-value (per inch)
of listed
material (
T
M
)
of listed material (
k
L
)
material (
T
L
)
T
M
(inches) =
k
M
x
T
L
*.84
T
M
(inches) = *.35
x
.75"
*.84
.312 (inches)=
.417
x
.75"
Answer - The minimum required thickness of the Micore 160 is .312"
therefore round up to nearest standard thickness available which is 3/8”
(.375”)
Minimum
r-value (per Inch)
Specified min.
thickness of = of listed material
x
thickness
alternate
r-value (per inch)
of listed
material
of alternate material
material
T
M
(inches) =
r
L
x
T
L
r
M
T
M
(inches) = *1.19 x
.75"
*2.86
.312 (inches)=
.416
x
.75"
Answer - The minimum required thickness of the Micore 160 is .312"
therefore round up to nearest standard thickness available which is 3/8”
(.375”)
Using the r formula:
Listed Material
k (per inch)
r (per inch)
Listed Min. Thickness
Listed Material
.84
K
L
1.19
r
L
3/4
"
(.75")
T
L
** Approved Alternate Materials for Floor/Hearth Protection
Alternative Materials
Thermal Values
Minimum Thickness
(rounded to nearest 1/8 inch)
k (per inch)
K
M
r (per inch)
r
M
Min. Thickness
T
M
Kaowool M Board
.47
2.13
.42" (1/2")
Micore 160™
U.S. Gypsum
.35
2.86
.31" (3/8")
Micore 300™
U.S. Gypsum
.46
2.17
.41" (1/2")
Durock™ Cement Board
U.S. Gypsum
1.92
.52
1.71" (1-3/4")
Hardibacker™
1.95
.51
1.74" (1-3/4")
Hardibacker 500™
2.30
.43
2.05" (2-1/8")
Cultured Stone Hearth-
stone™
2.82
.35
2.52" (2-5/8")
Wonderboard
3.23
.31
2.88" (3")
Super Firetemp M
Johns-Manville
.61
1.64
.54" (5/8")
Super Firetemp L
Johns-Manville
.54
1.85
.48" (1/2")
Face brick
9.00
.111
8.04" (8-1/8")
Common brick
5.00
.20
4.46” (4-1/2")
Cement mortar
5.00
.20
4.46” (4-1/2")
Ceramic tile
12.5
.08
11.16" (11-1/4")
Marble
~11
~.09
9.82" (9-7/8")
Table 2 - USA AND CANADA REQUIREMENTS
** If the hearth extension material(s) that is intended to be used is NOT listed
on Table 2, the material can still be used if the material(s) is noncombustible.
However, the manufacturer of the material must provide either the listed k-value
per inch or r-value per inch with listed thickness so that the minimum thickness
required for the hearth can be calculated (per instructions here or as specified
in the NFI Certification Manuals).
HEARTH PROTECTION
