Bellfires BCC-19, Installation Manual, Page: 17 / 34

How to determine if alternate floor protection materials are acceptable.
All floor protection materials must be non-combustible (i.e., metals, brick, stone, mineral fiber boards, etc.). Any organic
materials (i.e., plastics, wood, paper products, etc.,) are combustible and must not be used. The floor protector specified
may include some form of thermal designation such as R value (thermal resistance), k-factor (thermal conductivity), or
C-factor (thermal conductance).
Procedure:
1) Convert specification to R-value:
i.
R-value given–no conversion needed.
ii. K-factor is given with a required thickness (T) in inches: R = 1/k x T
iii. C-factor is given: R = 1/C
2) Determine the R-value of the proposed alternate floor protector.
i.
Use the formuli in step (1) to convert values not expressed as “R”.
ii. For multiple layers, add R-values of each layer to determine overall R-value.
3) If the overall R-value of the system is greater than the R-value of the specified floor protector, the alternate is
acceptable.
EXAMPLE:
The specified floor protector should be
w
” thick material with a k factor of 0.84. The proposed alternate is
4” brick with a C-factor of 1.25 over 8” mineral board with a k-factor of .29.
Step (a): Use formula above to convert specification to R-value.
R = 1/k x T = 1/ .84 x .75 = .893
Step (b): Calculate R of proposed system.
4” brick of C = 1.25, therefore Rbrick = 1/C = 1/1.25 = .80
8” mineral board of k = .29, therefore Rmin. Bd. = 1/.29 x .125 = .431
Total R = Rmineral board = .8 = .431 = 1.231
Step (c): Compare proposed system R of 1.231 to specified R of .893. Since proposed system R is greater than
required, the system is acceptable.
Definitions:
Thermal conductance = C = Btu = W
(hr)(ft2)(0F) (m2)(0K)
Thermal conductivity = k = (Btu)(in) = W = Btu
(hr)(ft2)(0F) (m)(0K) (hr)(ft)(0F)
Thermal resistance = R = (ft2)(hr)(0F) = (m2)(0K)
Btu W
Bellfires® BCC
17
Material
Insulboard 300™
Insulboard 230™
Insulboard 180™
Common brick
Cement mortar
Marble
Limestone
Ceramic Tile
(Btu)(in)
(hr)(ft
2
)(
0
F)
Typical materials that might be
substituted for hearth extensions
k in.
.458
.43
.34
5.00
5.00
11.00
6.5
12.5