Osburn 2200 OB02201 Installation And Operation Manual page 34

2200 Insert Installation and Operation Manual
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.
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.
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0.8 + 0.52 = 1.32.
Example:
K value = 0.75
Thickness = 1
R value = Thickness/K = 1/0.75 = 1.33
®
(R = 1 x 0.52 = 0.52).