Wall Shield Required
Where Less Than 12"
24"
30"
C
B
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.
Note: Also see NFI Certification Manuals for expanded explanation on calculating “R val- ues” when multiple materials are used.
5 1/2"
2" 
Max. Thickness Of Hearth Extension When
D
Figure 48
C A
WARNING: THE CRACK BETWEEN THE FIREPLACE AND THE HEARTH EXTEN- SION MUST BE SEALED WITH A NON-
Circulating Models Are On The Floor
Figure 50
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.”
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
COMBUSTIBLE MATERIAL.
WARNING: WHEN INSTALLING HEARTH EXTENSION IN FRONT OF A
7 1/2"
Max. Thickness Of Hearth Extension When
Figure 49
WARNING: WHEN INSTALLING THE HEARTH EXTENSION BE CAREFUL NOT TO BLOCK THE
WARNING: WHEN INSTALLING HEARTH EXTENSION IN FRONT OF A CIRCULAT- ING FIREPLACE MODEL, THE FIREPLACE MUST BE RAISED IF HEIGHT OF HEARTH EXTENSION EXCEEDS 2" ABOVE BOTTOM OF FIREPLACE (FIGURE 50 ).
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
Secure the hearth extension to the floor to prevent possible shifting.
FINISH TO YOUR TASTE
There are a wide variety of “finished looks” for 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.
Combustible materials may project beyond the sides of the fireplace opening as long as they are kept within the shaded areas illustrated in Figure 51.
Combustible |
|
|
|
Materials |
|
| Fireplace |
Allowed In |
|
| |
Shaded Area |
|
|
|
“Safe Zone” |
|
| 1" |
| 7" |
| |
|
|
| |
|
| 45° |
|
12" |
|
| Min. Distance To |
|
| 7" | |
|
| Protected Side Wall | |
|
|
| |
| 12" |
| Min. Distance To |
|
| Unprotected Side Wall | |
|
|
|
Figure 51