Osburn 1100 MODEL INSERT Owner's Manual page 13

The use of an R value is convenient when more than one material is going to be used in the hearth extension
to cover the combustible surface. This is because R values are additive, whereas K values are not. To find
the corresponding R factor to use for some selected materials, please see Table Thermal characteristics of
common floor protection materials in this section.
There are two ways to calculate the R factor 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 factor from R factors 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. To know the
R-values of some selected materials, see table Thermal characteristics of common floor protection
materials.
Example:
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
This R value is larger than the required 1.00 and is therefore acceptable
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 the R values of your proposed
materials as shown in the previous example.
INCHES
MILLIMETRES
*Refers to masonry fireplace opening.
0.8 + 0.52 = 1.32.
Example:
K value = 0.75
Thickness = 1
R value = Thickness/K = 1/0.75 = 1.33
Data for floor protection calculation
A
Smaller Bigger or
2 2
than 6 ft * = to 6 ft *
16" 20"
406 508
mm mm
B
(Note 1)
CAN: 18"
USA: 16"
CAN: 457 mm
USA: 406 mm
13
®
(R = 1 x 0.52 = 0.52).
C E
3 7/8" 9"
98 mm 229 mm
®