Focus Heterofocus 1400, Design Installation & Operating Manual, Page: 24 / 24

Page 24 of 24
Appendix.
How to determine if alternate floor protection materials are acceptable.
All floor protection 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 protection specified includes some form of thermal designation
such as R-value (thermal resistance) or k-factor (thermal conductivity).
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:
T
k
1
R
! =
iii. K-factor is given with a required thickness (T) in inches:
T
12 x K
1
R
! =
iv. r-factor is given with a required thickness (T) in inches:
R = r x T
2. Determine the R-value of the proposed alternate floor protector.
i. Use the formula 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 3/4-inch thick material with a k-factor of
0.84. The proposed alternate is 4” brick with an r-factor of 0.2 over 1/8” mineral board with a
k-factor of 0.29.
Step (a): Use formula above to convert specification to R-value.
893 . 0 75 . 0 x
84 . 0
1
T
k
1
R
= = ! =
Step (b): Calculate R of proposed system.
4” brick of r = 0.2, therefore:
431 . 0 4 x 2 . 0
rick b
R
= =
1/8” mineral board of k = 0.29, therefore
431 . 0 125 . 0 x
29 . 0
1
board mineral
R
= =
R
total
= R
brick
+ R
mineral board
= 0.8 + 0.431 = 1.231
Step (c): Compare proposed system R
total
of 1.231 to specified R of 0.893. Since proposed
system R
total
is greater than required, the system is acceptable.
DEFINITIONS:
Btu
) F
o
)( hr )(
2
(ft
R
=
12 x K
) F
o
)( hr )(
2
ft (
(Btu)(in)
k
= =
) F
o
)( hr )(
2
ft (
(Btu)(ft)
K
=
k
1
) in )( Btu (
) F
o
)( hr )(
2
(ft
r
= =