Note: Any noncombustible material whose k value is less than .84 or whose r value is more than 1.19 is acceptable.
If the fireplace is installed on a combustible floor, use the metal safety strips (provided) on the floor extending half under the fire- place and half under the hearth extension (refer to Figures 6 & 7).
A wall shield is required where a continuous perpendicular side wall is within 12" of the fireplace opening (Figure 46 ). Use a 36" W x 36" H wall shield constructed of a durable, noncombustible material having an equal or better (lower k value) insulating value than k =
.54 BTU IN/FT2 HR ° F. At no time may a perpendicular side wall be located closer than 9" from the fireplace opening.
If fireplace is installed diagonally across a 90° corner; no wall shields are required.
Wall | Side Wall cannot | |
be Closer than 12" | ||
Shield | ||
(305mm) under | ||
| ||
| any Circumstances |
C
B
If it is desired to elevate a marble hearth ex- tension to a level of 5” or more above the floor surface. What combination of noncombus- tible materials can be used to accomplish this?
If common brick is used so that the 3 1/2” dimension is the height, “R” for the common brick becomes:
brick
“R”M = rM x TS = 0.20 x 3 1/2" = .70
Using 1/2” of mortar to set the brick, “R” for the mortar is calculated as follows:
mortar
“R”M = rM x TS = 0.20 x 1/2" = .10
Next, a 3/4" marble slab set in 1/2" mortar cov- ers the brick, “R” for the marble and mortar becomes:
marble
“R”M = rM x TS = 0.05 x 3/4" = .038
mortar
“R”M = rM x TS = 0.20 x 1/2" = .10
The sum of all “R values” is: .70 + .10 +. 038 + .10 = .938
This would NOT be an acceptable combination of material for the hearth extension since the total calculated “R value” of the materials used is under the required “R value” of 1.19. An additional layer of insulating materials must be used.
(197mm)
Max. Thickness of Hearth Extension when LBR Models are on the Floor
Figure 47
Max. Thickness of Hearth Extension when LBC Models are on the Floor
Figure 48
Secure the hearth extension to the floor to prevent possible shifting.
D
Figure 46
C A
Note: Also see NFI Certification Manuals for expanded explanation on calculating “R val- ues” when multiple materials are used.
FINISH TO YOUR TASTE
There are a wide variety of “finished looks” for
18
Calculating Minimum Thickness if Multiple Materials are Used
At times it is important to know what combination of materials are acceptable for use as floor protection. The “R values” are used to determine acceptable combinations of materials because “R values” are additive where r and k values are not.
“R value” = 1/k = “r” x thickness of material used
Example: Given that the required “R value” for a suitable floor protector used must be equal to or greater than:
“R” = rL x TL = 1.19 x 1” = 1.19.”
WARNING: THE CRACK BETWEEN THE FIREPLACE AND THE HEARTH EXTEN- SION MUST BE SEALED WITH A NON- COMBUSTIBLE MATERIAL.
WARNING: WHEN INSTALLING HEARTH EXTENSION IN FRONT, THE FIREPLACE MUST BE RAISED IF HEIGHT OF HEARTH EXTENSION EXCEEDS
(LBR MODELS) ABOVE THE BOTTOM OF FIREPLACE (FIGURE 47 ).
WARNING: THE FIREPLACE MUST BE RAISED IF THE HEIGHT OF THE HEARTH EXTENSION EXCEEDS
(LBC MODELS) ABOVE THE BOTTOM OF THE FIREPLACE (FIGURE 48 ).
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
these fireplaces, from formal wall decor with elaborate mantels to rustic wood paneling or warm brick facings.
Only noncombustible materials like stone, tile, brick, etc., may overlap the black front facing. Do not extend these materials beyond the black facing and into the firebox area. Be sure not to interfere with the installation and operation of glass doors or block the upper or lower grilles. Seal all joints between the black facing and wall surrounds to prevent air intrusion. Use non- combustible caulking material only to seal the black metal facing to the surround material on the finished wall.
