Hearth and Home Technologies 36, 42 owner manual Finishing, Hearth Extension

8Finishing

A. Hearth Extension				WARNING
A hearth extension must be installed with all fireplaces to
protect the combustible floor in front of the fireplace from				Fire Risk
both radiant heat and sparks. See Figures 8.1­‑8.3.
				• Metal hearth strips MUST be installed.
	Continuous,			Sparks or embers may ignite flooring.
1/2 in. Micore	non-combustible sealant	Fireplace
	non-combustible material		Protective
insulation
Hearth Ext	Tile, stone or other
or equivalent
(see Table 11.2)			Metal Hearth
			Strip

2 in. (51 mm)

Floor constructed of wood or required other combustible material

Figure 8.1 Hearth Extension Construction 1 in. (25 mm)

overlap

The hearth extension should slope away from the front of the
fireplace and chase at 1/8 in. to 1/4 in. per foot. Spark strips
must be used on top of any combustible hearth materials
	Protective metal strips are placed 2 in. (51 mm) under the
used for moisture management.
	front of the fireplace and must extend beyond the front
This fireplace has been tested and approved for use with a	and sides of fireplace opening by 2 in. (51 mm).
hearth extension insulated to a minimum R value of 1.03.	Figure 8.2 Positioning the Protective Metal Hearth Strips
To substitute materials for the factory-available hearth ex-
tensions, see Figure 8.3 and calculate insulation alterna-	WARNING
tives as per Table 8.1 and the following formulas:
• Thermal conductivity per inch thickness = k	Fire Risk
• k = (BTU)(inch) / (foot2)(hour)(°F)	• Hearth extensions must be installed
• Required thickness = Rk	exactly as specified.
• Thermal resistance per inch thickness = r	High temperatures or hot embers may ignite
	concealed combustibles.

• r = (foot2)(hour)(°F) / (BTU)(inch)

• Required thickness = R / rB.

Table 8.1
Hearth Extension Insulation Alternatives-Total minimum R Value must equal 1.03
			Minimum
	k per inch	r per inch	thickness
Material	thick	thick	required
Hearth & Home HX3, HX4 (Micore 300™)	0.49	2.06	1/2 in.			A		B
USG Micore 160™	0.39	2.54	1/2 in.				C
USG Durock™ Cement Board	1.92	0.52	2 in.
Cement Mortor	5.0	0.20	5-1/8 in.
Common Brick	5.0	0.20	5-1/8 in.	CAT. #		A	B	C
Ceramic Tile	12.50	0.08	12-1/4 in.
				HX3	in	52	16	8
Armstrong™ Privacy Guard Plus	0.46	2.18	1/2 in.
Marble	14.3-20.0	0.07-0.05	14-5/8 in. - 20-3/8 in.		mm	1321	406	203
				HX4	in	66	20	12
					mm	1676	508	305
				Figure 8.3 Hearth Extension Dimensions

Outdoor Lifestyles by Hearth & Home Technologies Inc. • Montana US-CAN • 4039-156 Rev K • 7/11 23