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:
0.25x 1.0" = 0.30" thickness required
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
Mantels
A mantel may be installed if desired (see Figure 4). Woodwork such as wood trims, mantels or any other combustible material projecting from the front face must not be placed within 12" of the fireplace open- ing. Combustible materials above 12" and projecting more than 1 1/2" from the fireplace must not be placed less than 15" from the top opening of the fireplace (NFPA STD 211, Sec.
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.
|
| Combustible |
| 12 1/4" Ref. | Material |
|
| Safe |
6" |
| Zone for |
Ref. | 33° | Projection of |
| Combustible | |
|
| |
| 3" Nom. | Materials |
|
|
11/2" Max.
15" Min.
12" Min. | Upper |
|
Section of
Fireplace
Fireplace
Opening
Ember Protector
Fireplace Front
Raised Hearth
Ember Protector 
Fireplace Front
Elevated
Ember Protector
Top View of Fireplace
|
| FIREBOX | |
| 7.75" |
| |
|
| 3" Max. | |
Hearth | SAFE ZONE | 4.5" | |
33° | |||
Extension |
| ||
Seal Gap | Min. to | Combustible | |
| Perpendicular | ||
| Material Must | ||
| Side Wall | ||
| Not Overlap | ||
| 12" | ||
| Front Face | ||
|
|
Figure 3 - Hearth Extension | Figure 4 - Mantel Clearances to |
| |
| Combustible Material |
www.desatech.com109493-01N
