Desa (V)gM42h Fireplace Installation, Continued, Hearth Extension, Mantels, Mantel Clearances to

Fireplace Installation

Continued

Hearth Extension

A hearth extension projecting a minimum of 20" in front of and a minimum of 12" beyond each side of the fireplace opening is required to protect combustible floor construction in front of the fire- place. Fabricate a hearth extension using a material which meets the following specifications: a layer of noncombustible, inorganic material having a thermal conductivity of K=0.84 BTU IN/FT, HR. F (or less) at 1" thick. For example, if the material selected has a K factor of 0.25, such as glass fiber, the following formula would apply:

0.25 x 1.0" = 0.30" thickness required

0.84

Mantels

A mantel may be installed if desired (see Figure 4). Woodwork such as wood trims, mantels or any oth- er combustible material projecting from the front face must not be placed within 12" (GM36) or 18" (GM42/50) of the fireplace opening. Combustible materials above 12" (GM36) or 18" (GM42/50) and projecting more than 1 1/2" from the fireplace must not be placed less than 15" (GM36) or 21" (GM42/50) from the top opening of the fireplace (NFPA STD 211, Sec. 7-3.3.3).

Mantels or any other combustible material also may come up to the side edge of the black metal face of the fireplace just as long as the projection from the front face fall within the limit shown in Figure 4.

Thermal conductivity "K" of materials can be obtained from the manufacturer or supplier of the noncombustible material. If the hearth extension is to be covered, use noncombustible material such as tile, slate, brick, concrete, metal, glass, marble, stone, etc. Provide a means to prevent the hearth extension from shifting and seal gap between the fireplace frame and hearth extension with a non- combustible material (see Figure 3).

WARNING: Hearth extension

is to be installed only as shown

in Figure 3.

Seal Gap

Fireplace Front

Ember Protector

12 1/4" Ref.

6"
Ref.	33°

3" Nom.

15" Min.

(GM36) 11/2" Max. 21" Min.

(GM42/50)

12" Min. (GM36)

18" Min. (GM42/50)

Fireplace

Opening

Combustible

Material

Safe

Zone for

Projection of

Combustible

Materials

Upper

Section of

Fireplace

Fireplace Front
Raised Hearth
Ember Protector	Hearth
	Extension
Fireplace Front	Seal Gap
Elevated

Ember Protector

Figure 3 - Hearth Extension

Top View of Fireplace

7.75" (GM36)	FIREBOX
11.5" (GM42/50)
	3" Max.
SAFE ZONE	4.5"
33°
Min. to	Combustible
Perpendicular
	Material Must
Side Wall
	Not Overlap
12" - GM36
	Front Face
18" - GM42/50

Figure 4 - Mantel Clearances to

Combustible Material

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