New Buck Corporation 81 ユーザーズマニュアル

 
 

1.  The hearth must be of masonry construction and  must extend a  minimum of 16” in front of 
the firebox opening and  a  minimum of 8" to either side of  the firebox opening. 
 
2.   If there is not minimum hearth protection from the front of  the firebox opening and the 
front of the masonry hearth, a  floor protector must be used in front of the hearth  to 
protect  combustible materials.  The floor protector must be 3/8" minimum thickness non-
combustible material or equivalent. 
 
With the floor protector or hearth extension material specified as one layer of 2" thick brick 
with a K* factor of 5.0, you may use alternate materials as long as the K* factor (s) is calculated 
as follows: 
 

FORMULA: Required thickness = (K of alternate material/K of millboard) X (thickness 

of millboard) 
 
 

EXAMPLE:  An alternate inorganic non-combustible millboard with a K* of .9375 

would require a thickness as follows: 
 

 

Required thickness = (.9375/5.0) x 2 in. 

 

 

 

 

       = 3/8 inch 

 
K* FACTORS OF ALTERNATE MATERIALS 
 
Material 

Ceroform 

126 

    .21 

   1/8" 

Limestone 

    8.0 

   3.2" 

Concrete 

    8.0 

   3.2" 

Sandstone 

    13.0 

   5.2" 

Marble 

     18.0 

   7.2" 

 
Hearth extension or floor protector thickness above four (4) inches are generally not acceptable 
due to cost, floor load capacity, and look.  The alternate we recommend is using Ceroform No. 
126 millboard 1/8"  minimum and putting any type decorative brick or stone (any thickness) on 
top of it. 
 
*  The K*  factor represents the thermal conductivity of a material and is the time rate of heat 
flow through a homogeneous material under steady-state conditions, through unit area, per unit 
temperature gradient in the direction perpendicular to a surface. 
 

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