Flame Energy XTD 1.9 Installation And Operation Manual page 37

XTD 1.9 Insert Installation and Operation Manual
If the extension of the masonry hearth is raised at least 4" from the floor protection, a non-
combustible material without an R factor is sufficient.
If non-combustible material floor protection needs to be added in front of and level with the
hearth extension of the masonry fireplace, an R factor equal to or greater than 2.00 is
required.
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.
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