Lennox Hearth RDI-36-H Hearth Extension Dimensions, Wall Shield, For the alternate, Minimum, 273

Hearth Extension Dimensions

A

16"

B

33"

C

8"

D

49"

C

B

C

Note: To convert inches to millimeters

A

divide by 0.03937

D

Figure 48

Methods of Determining Hearth Extension

and

Wall Shield

Answer - The minimum

required thickness of the Micore 160 is .273”,

Equivalents - To determine the thickness required

for the alternate

therefore round up to 1/4”

and use the nearest standard thickness available

material when either the “k” value or “r” value is

known, use either the

which is 1/2”.

k formula or r formula.

Listed Material

Example: If Micore 160 is to be used for the hearth extension fireplace, how

k (per inch)

r (per inch)

Listed Min.Thickness

thick must this material be?

Listed Material

1.28

0.78

1"

kM = k value per inch of alternate material

KL

rL

TL

** Approved Alternate Materials for Floor/Hearth Protection

rM = r value per inch of alternate material

TM =

minimum thickness required for alternate material

AlternativeMaterials

Thermal Values

MinimumThickness

TS =

standard thickness of the alternate material

(rounded to nearest 1/8 inch)

k (per inch)

r (per inch)

Min. Thickness

kL = k value per inch of listed material

KM

rM

TM

Kaowool M Board

.47

2.13

.37" (3/8")

rL = r value per inch of listed material

TL = minimum thickness of listed material

Micore 160™

.35

2.86

.27" (1/4")

U.S. Gypsum

Note: An asterix “*” indicates, it is a value taken from Table 1.

Micore 300™

.46

2.17

.36" (3/8")

Using the k formula:

U.S. Gypsum

Durock™ Cement Board

1.92

.52

1.50" (1-1/2")

Minimum

k-value (per Inch) of

Specified min.

U.S. Gypsum

thickness of

=

alternate material (kM) x

thickness

Hardibacker™

1.95

.513

1.52" (1-1/2")

alternate

k-value (per inch)

of listed

Hardibacker 500™

2.30

.435

1.80" (1-3/4")

material (TM)

of listed material (kM)

material (TL)

Cultered Stone Hearth-

2.82

.355

2.20" (2-1/4")

TM (inches)

=

kM

x

TL

stone™

Wonderboard

3.23

.31

2.52" (2-1/2")

*1.28

Super Firetemp M

.61

1.64

0.48" (1/2")

TM (inches)

=

*.35

x

1"

Johns-Manville

*1.28

Super Firetemp L

.54

1.85

0.42" (3/8")

Johns-Manville

.273

(inches) =

.273

x

1"

Face brick

9.00

.111

7.03" (7")

Answer - The minimum required thickness of the Micore 160 is .273”,

Common brick

5.00

.20

3.91" (3-7/8")

Cement mortar

5.00

.20

3.91" (3-7/8")

therefore round up to 1/4” and use the nearest standard thickness

available which is 1/2”.

Ceramic tile

12.5

.08

9.77" (9-3/4")

Using the r formula:

Marble

11.0

.09

8.59" (8-5/8")

Table 1

Minimum

r-value (per Inch)

Specified min.

thickness of

=

of listed material

x

thickness

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

alternate

r-value (per inch)

of listed

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

material

of alternate material

material

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

TM (inches)

=

rL

x

TL

thickness required for the hearth can be calculated (per instructions on this

Page and/or as specified in the NFI Certification manuals).

rM

TM (inches)

=

*0.78

x

1"

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

other acceptable calculation methods and acceptable alternate materials

*2.86

which can be used.

.273

(inches) =

.273

x

1"

17

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.