Lennox Hearth CR-3835R Finish to Your Taste, Value = 1/k = r x thickness of material used, Model

20

		If Less Than 12"
	40"	(305mm) Wall
		Shield Required
(1016mm)
		Wall Shield
	Wall	Not Required
40"	Shield	On This Wall
(1016mm)
Metal Safety
Strip	20"
		20"
	(508mm)	(508mm)

Inside Corner

Figure 44

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

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.

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 OF A NON-CIRCU- LATING FIREPLACE MODEL, THE FIRE- PLACE MUST BE RAISED IF HEIGHT OF HEARTH EXTENSION EXCEEDS 7" ABOVE THE BOTTOM OF FIREPLACE (FIGURE 45 ).

6"

Max. Thickness Of Hearth Extension

When Models Are On The Floor

Figure 45

Secure the hearth extension to the floor to prevent possible shifting.

NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.

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 46.

Combustible
Materials
Allowed In					Fireplace
Shaded Area
“Safe Zone”	11	⁷⁄₈”
					8"
			45°
15 ⁷⁄₈”				Min. Distance To
			8"
				Protected Side Wall
	12"			Min. Distance To
				Unprotected Side Wall
Figure 46
Model		Part Number			Weight
CR-3835R			P/N 015014		210 lbs.
CR-3835L			P/N 015013		210 lbs.