Owner`s manual

12
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
®
(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
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.
Example:
K value = 0.75
Thickness = 1
R value = Thickness/K = 1/0.75 = 1.33
The more extended the insert, the greater the heat transfer to the room. You may install the insert within the
minimum and maximum extension listed in the table below (value (C)) or any position in between. The
position chosen will depend on your own preference for most installations, your current configuration, the
compliance with the preceding installation instructions and compliance with the building code requirements.
To determine the minimum and maximum protrusion of the insert, refer to table Data for floor protection
calculation.