Lennox Hearth 20 FS-2, 30 FS-2 manual 5

Floor Protection - ProÞle¨ 30 FS-2

Minimum

k-value (per Inch) of

SpeciÞed min.

thickness of

=

alternate material (kM)

x

thickness

The floor protector must meet or exceed the minimum thermal require-

alternate

k-value (per inch)

of listed

material (TM)

of listed material (kL)

material (TL)

ments as defined on this page (see Floor Protection / Hearth Extension

kM

Using Alternate Material As Floor Protector). If the floor protection is

TM (inches)

=

x

TL

to be stone, tile, brick, etc., it must be mortared or grouted to form a

*.84

continuous noncombustible surface. If a chimney connector extends

TM (inches)

=

*.46

x

.375"

horizontally over the floor, protection must also cover the floor under

*.84

the connector and at least 2” (51 mm) to either side.

.205 (inches)=

.547

x

.375"

The floor protector must fully cover the area beneath the appliance and

Answer - The minimum required thickness of the Micore 300 is .205," there-

extend 6” to the front, 6” to the sides, and 6” from the back as shown

in Figure 1 (Note: When installed at clearances less than 6”, the floor

fore round up to nearest standard thickness available which is 1/4."

protection is only required to extend to the wall).

Using the r formula:

Floor Protection / Hearth Extension Using Alternate Material As

Minimum

r-value (per Inch)

SpeciÞed min.

thickness of

=

of listed material

x

thickness

Floor Protector - All Models

alternate

r-value (per inch)

of listed

Note: Also see Floor Protection above for free-standing models and Hearth

material

of alternate material

material

TM (inches)

=

rL

x

TL

Requirements, Page 7 for the fireplace insert model.

rM

The hearth pad or alternate material used as a floor/hearth protector

TM (inches)

=

*1.19

x

.375"

must be constructed of a durable noncombustible material having an

* 2.17

equal or better thermal conductivity value (lower k value) of k = .84 BTU

.205 (inches)=

.548

x

.375"

/ IN FT2 HR °F or a thermal resistance that equals or exceeds r = 1.19

Answer - The minimum required thickness of the Micore 300 is .205," there-

HR °F FT2 IN/BTU with a minimum thickness of 3/8”. With these values,

determine the minimum thickness of the alternate material required using

fore round up to nearest standard thickness available which is 1/4."

the formula(s) and the table shown here (see Table 1).

Listed Material

Note: Any noncombustible material having a minimum thickness of 3/8”

k (per inch)

r (per inch)

Listed Min.Thickness

(10 mm) whose k value is less than .84 or whose r value is more than

Listed Material

.84

1.19

3/8" (.375")

1.19 is acceptable. If the alternate material used has a higher k value

KL

rL

T

L

or lower r value will require a greater thickness of the material used. In

** Approved Alternate Materials for Floor/Hearth Protection

some cases, if the k value is less or the r value higher, a thinner material

AlternativeMaterials

Thermal Values

MinimumThickness

may be used.

(rounded to nearest 1/8 inch)

Methods of determining ßoor protection equivalents:

k (per inch)

r (per inch)

Min. Thickness

KM

rM

TM

To determine the thickness required for the alternate material when

Kaowool M Board

.47

2.13

.21" (1/4")

either the "k" value or "r" value is known, use either the k formula or r

formula.

Micore 160ª

.35

2.86

.16" (1/8")

Example: If Micore 300 is to be used for the floor protection, how thick

U.S. Gypsum

Micore 300ª

.46

2.17

.21" (1/4")

must this material be?

U.S. Gypsum

kM = k value per inch of alternate material

Durockª Cement Board

1.92

.52

.86" (7/8")

rM = r value per inch of alternate material

U.S. Gypsum

Hardibackerª

1.95

.513

.87" (7/8")

TM =

minimum thickness required for alternate material

TS =

standard thickness of the alternate material

Hardibacker 500ª

2.30

.435

1.03" (1")

Cultered Stone Hearth-

2.82

.355

1.26" (1-1/4")

kL = k value per inch of listed material

stoneª

rL = r value per inch of listed material

Wonderboard

3.23

.31

1.44" (1-1/2")

TL = minimum thickness of listed material

Super Firetemp M

.61

1.64

.27" (1/4")

Note: An asterisk "*" indicates, it is a value taken from Table 1.

Johns-Manville

Super Firetemp L

.54

1.85

.24" (1/4")

Using the k formula:

Johns-Manville

** If the hearth extension material(s) that is intended to be used is NOT listed

Face brick

9.00

.111

4.02" (4")

on Table 1, the material can still be used if the material(s) is noncombustible.

Common brick

5.00

.20

2.23" (2-1/4")

However, the manufacturer of the material must provide either the listed k-value

Cement mortar

5.00

.20

2.23" (2-1/4")

per inch or r-value per inch with listed thickness so that the minimum thickness

required for the hearth can be calculated (per instructions on this page and/or

Ceramic tile

12.5

.08

5.58" (5-5/8")

as specified in the NFI Certification Manuals).

Marble

~11

~.09

4.91" (4-7/8")

Note: Also see NFI (National Fireplace Institute) Certification Manuals show-

Table 1

ing other acceptable calculation methods and acceptable alternate materials

which can be used.

5

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE