Hearthstone Quality Home Heating Products, Inc
® Green Mountain Insert 70 (Model 8450)
12
Figure 7
– Installation More Than 5”
R-V
ALUE
There are two ways to calculate the R-value of the
floor protection. First, by adding the R-values of
materials used, or by the conversion if the K factor
and thickness of the floor protection are given.
To calculate the total R value from R values of the
materials used, simply add the R-values of
materials. If the result is equal to or greater than the
R-value requirements, the combination is
acceptable. R-values of some selected materials
are shown below:
Table: Thermal Characteristics of Common Floor
Protection Materials*
MATERIAL
CONDUCTIVITY
(k) PER INCH
RESISTANCE (R)
PER INCH
THICKNESS
Micore
®
160
0.39
2.54
Micore
®
300
0.49
2.06
Durock
®
1.92
0.52
Hardibacker
®
1.95
0.51
Hardibacker
®
500
2.3
0.44
Wonderboard
®
3.23
0.31
Cement mortar
5.00
0.2
Common brick
5.00
0.2
Face brick
9.00
0.11
Marble
14.3
– 20.00
0.07
– 0.05
Ceramic tile
12.5
0.008
Concrete
1.050
0.950
Mineral wool
0.320
3.120
insulation
Limestone
6.5
0.153
Ceramic board
(Fibremax)
0.450
2.2
Horizontal still air**
(1/8")
0.135
0,920**
* Information as reported by manufacturers and
other resources
**Horiz
ontal still air can’t be ‘stacked’ to accumulate
R-values; each layer must be separated with
another non-combustible material.
Example 1:
Required floor protection R of 1.00. Proposed
materials: four inches of brick and one inch of
Durock® board.
Four inches of brick (R = 4 x 0,2 = 0,8) plus 1 inch
of Durock® (R = 1 x 0.52 = 0.52).
0.8 + 0.52 = 1.32. This R value is larger than the
required 1.00 and is therefore acceptable.
Example 2:
In the case of a known K and thickness of
alternative materials to be used in combination,
convert all K values to R by dividing the thickness of
each material by its K value. Add R values of the
proposed materials as shown in the previous
example.
Example:
Common brick K value = 5
Thickness = 4"
R value = Thickness/K = 4/5 = 0.8
Durock K value =1.92
Thickness = 1"
R value = Thickness/K = 1/1.92 = 0.52
Total R value = .8 + 0.52 = 1.32
