Lenoxx Optima 3 FS Manuale Utente

PAGE 6 

The floor protector must 

meet or exceed the 

minimum thermal re-

quirements as defined 

on this page (see Floor 

tector). If the floor pro-

tection is to be stone, 

tile, brick, etc., it must 

be mortared or grouted 

to form a continuous 

noncombustible sur-

face. If a chimney con-

nector extends horizon-

tally over the floor, pro-

tection must also 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 appli-
ance and extend 6” to the front, 6” to the sides, and 6” from the 
back as shown in the illustration to the right (Note: When installed 
at clearances less than 6”, the floor protection is only required to 
extend to the wall).

 

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, deter-
mine 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: 

 

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 be-

cause “R values” 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 

protector used must be equal to or greater than “R” = r x T

L

 = 

1.19 x .375” = .45. 

 

 

 

 

 

 

 

 

 

↓ 

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 ma-
terial must provide either the listed k-value per inch or r-value per 
inch and the minimum acceptable thickness will need to be calcu-
lated per instructions on this page.

 

. 

*Up to 6”  

1          53 mm minimum 

6”/ 

153mm

min. 

6”/ 

153mm 

min. 

 

6”/153mm 

minimum 

 

 

 

 

 

 

 

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