Lennox Hearth II-T C FS - Manual (Page 5)

PLANNING YOUR INSTALLATION
PAGE 5
FLOOR PROTECTION – Advantage II-T C FS
(For USA and Can-
ada) This appliance
requires 3/8" (10
mm) minimum non-
combustible floor
protection designed
for solid fuel burning
appliances having a
thermal conductivity
of k = .84 BTU in/ft
or equivalent. If the
floor protection is to
be stone, tile, brick,
etc., it must be mor-
tared or grouted to
form a continuous
non-combustible sur-
face (See Using Alternate Material As Floor Protector below).
If a chimney connector extends horizontally over the floor,
protection must cover the floor under the connector and at
least 2" (51 mm) to either side. The floor protector must fully
cover the area beneath the appliance and extend 6” to the
front, 6” to the sides, and up to 6” from the back (see illustra-
tion above and following note).
*Note: When installed at clearances less than 6”, the floor
protection is only required to extend to the wall.
FLOOR PROTECTION / HEARTH EXTENSION USING AL-
TERNATE MATERIAL AS FLOOR PROTECTOR (also see
Floor Protection above for freestanding models and Hearth
Requirements, page 8 for the insert model)
The hearth pad or alternate material used as a floor/hearth
protector must be constructed of a durable noncombustible
material having an equal or better thermal conductivity value
(lower k value) of k = .84 BTU / IN FT
2 HR °F or a thermal
resistance that equals or exceeds r = 1.19 HR °F FT 2 IN/BTU
with a minimum thickness of 3/8”. With these values, determine
the minimum thickness of the alternate material required using
the formula(s) and the table shown here (see chart - Approved
Alternate Materials for Floor/Hearth Protection).
Note: Any noncombustible material having a minimum thickness
of 3/8” (10 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: Durock  Cement is to be used for the floor protec-
tion. How thick must this material be? The following formulas
give the means of determining minimum thickness required.
T
M
= minimum thickness required for alternate material
k
M
= k value per inch of alternate material
T
L
= minimum thickness of listed material
r
M
= r value per inch of alternate material
Using the k formula:
Minimum k-value (per Inch) Specified min.
thickness of = of alternate material x thickness
alternate k-value (per inch) of listed
material of listed material material
T
M
(inches) = k
M
x T
L
.84
T
M
(inches) = 1.92 x .375 (3/8”)
.84
Answer using k: 2.29 x 0.375” = 0.858 = ~7/8”
7/8” thickness (minimum) Durock
 Cement will be required.
Using the r formula:
T
M
(inches) = 1.19 x T
L
r
M
T
M
(inches) = 1.19 x 375 (3/8”)
.52
Answer using r: 2.29 x 0. 375” = 0.858 = ~7/8”
7/8” thickness (minimum) Durock
 Cement will be required.
At times it is important to know what combination of materials are
acceptable for use as floor protection. The “R values” are used to
determine acceptable combinations of materials because “R val-
ues” are additive where r and k values are not.
“R value” = 1 = r x thickness of material used
k
Example: Given that the required “R value” for a suitable floor pro-
tector used must be equal to or greater than “R” = r x T
L
= 1.19 x
.375” = .45.
Approved Alternate Materials for
Floor/Hearth Protection (**)
Alternative
Materials
↓
Thermal Values * Minimum
Thickness
k (per inch) r (per inch) T
M
Kaowool M Board .47 2.13 * 3/8”
Micore 160  .35 2.86 * 3/8”
Micore 300  .46 2.18 * 3/8”
Durock  Cement 1.92 .52 7/8”
Hardibacker  1.95 .51 7/8”
Hardibacker 500  2.30 .44 1 1/8”
Cultered Stone
Hearthstone

2.82 .35 1 5/8”
Wonderboard 3.23 0.31 1 1/2”
Face brick 9.00 0.11 4 1/8”
Common brick 5.00 0.20 2 1/4”
Cement mortar 5.00 0.20 2 1/4”
Ceramic tile 12.5 .08 5 5/8”
Marble ~ 20.0 ~ .05 9”
Note: To convert inches to millimeters divide by .03937.
* After minimum thickness is calculated, the thickness can be no
less than 3/8” (.375” / 10mm).
(**) If the floor protector to be used is a noncombustible material and is
NOT listed on the chart above, the manufacturer of the material must
provide either the listed k-value per inch or r-value per inch and the
minimum acceptable thickness will need to be calculated per instruc-
tions on this page.
Top View
6”
153 mm
6”
(153mm)
min.
Listed Material
Thermal Values Specified
Minimum
Thickness
k (per inch) r (per inch) T
L
Listed Material → .84 1.19 3/8” (.375)
6”
153 mm
6”
(153mm)
min.
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