Stratford
Fireplace Installation and Operation Manual
36 __________________________________________________________________________
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 6.2.2:
Minimum Hearth 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
6.2.3
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
