Osburn OB04002 - Manual (Page 40)

Stratford Fireplace Installation and Operation Manual
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A noncombustible floor protection with R value insulation equal to or greater than 1.00 must be
installed in front of the unit. For more details see Section 6.3.2: Minimum Heart Extension
Requirements. 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 Thermal Characteristics of Common Floor Protection Materials table.
CAUTION: DO NOT LEAVE CARPET UNDER THE FLOOR PROTECTION IN FRONT OF THE FIREPLACE
6.3.1.3 R Calculations
There are two ways to calculate the R factor of the floor protection. First, by adding the R-values
of the proposed materials or if some K and thickness values are given, by converting them to R
values.
To calculate the R factor for a composite floor protection made of a combination of alternative
materials, simply add the R-values of those materials. If the result is equal to or larger than the
required R value, the combination is acceptable. For R-values of some selected materials, see
Appendix section.
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