Hearth and Home Technologies NorthStar-BK, NorthStar-GT, NorthStar-NT Finishing, Hearth Extension

8 Finishing

A. Hearth Extension

A hearth extension must be installed with all fireplaces to protect the combustible floor in front of the fireplace from both radiant heat and sparks. See Figures 38.1 below, and Figures 40.1 and 40.2 on page 40.

	High temperature
	(300°F min.) continuous,
HX3 or HX4	non-combustible sealant		Fireplace
	non-combustible material			Protective
insulation
Hearth Ext	Tile, stone or other
or equivalent
(see Table below)				Metal Hearth
				Strip
		2 in. (51 mm)
Floor constructed of wood or		required
other combustible material

Figure 38.1 Hearth Extension Construction

WARNING

Fire Risk

•Maintain clearances.

•Use only non-combustible material below standoffs, material such as cement board is acceptable.

•Framing or finishing material used on the front of, or in front of, the appliance closer than the minimums listed, must be constructed entirely of noncombustible materials (i.e., steel studs, concrete board, etc.).

B. Calculating Alternate Floor Protection

Material

Thermal Conductivity: k value

The k value indicates the amount of heat (in BTU’s) that will flow in 1 hour through 1 square foot of a uniform material 1 inch thick for each degree (F) of temperature difference from one side of the material to the other. The LOWER the k factor means less heat is being conducted through the non-combustible material to the combustible material beneath it. The k value of a mate- rial must be equal or smaller then the required k value to be acceptable.

(BTU) (inch) (foot2 (hour) (oF)

Thermal Resistance: R value

The R value is a measure of a material’s resistance to heat transfer. R value is convenient when more than one material is used since you can add the R values together,

whereas you can not do this for k value. The HIGHER the R factor means less heat is being conducted through the non- combustible material to the combustible material beneath it. The R value of a material must be equal or larger then the required R value to be acceptable.

Converting k to R:

Divide 1 by k and multiply the results times the thickness in inch- es of the material.

R = 1/k x inches of thickness

Converting R to k:

Divide the inches of thickness by R.

k = inches of thickness/R

Calculations:

Example: Floor protection requires k value of 0.84 and 3/4 inch thick.

Alternative material has a k value of 0.6 and is 3/4 inch thick.

Divide 0.6 by .75 = k value of 0.80. This k value is smaller than 0.84 and therefore is acceptable.

Table 38.1

Hearth Extension Insulation Alternatives

Minimum R Value = 2.18

			Minimum
Material	k per inch	R per inch	thickness
	thick	thick	required
Hearth & Home HX3, HX4	0.49	2.18	1 in.
USG Micore 300™	0.49	2.18	1 in.
USG Durock™ Cement Board	1.92	0.52	2-1/4 in.
Cement Mortor	5.0	0.20	5-7/8 in.
Common Brick	5.0	0.20	5-7/8 in.
Ceramic Tile	12.50	0.08	14-5/8 in.
Armstrong™ Privacy
Guard Plus	0.46	2.18	1/2 in.
Marble	14.3-20.0	0.07-0.05	16-5/8 in. - 23-3/8 in.

Page 38 Heat & Glo • NorthStar EPA Fireplace • 480-1081C September 1, 2008