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The hearth and/or floor protection must be a thermally rated non-com-
bustible hearth/floor protector meeting or exceeding a thermal rating of
k=.84 or equivalent with a listed thickness of 3/4" (19mm) minimum in
USA and Canada. The covering must extend 24” (610mm) in front of the
heater and 8” (200mm) to either 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) = kM 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 1, 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).
Note: Also see NFI (National Fireplace Institute) Certification Manuals show
-
ing other acceptable calculation methods and acceptable alternate materials
which can be used.
HEARTH PROTECTION