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16
Vermont Castings EWF30
20008662
The top of insulation must be covered with a non-com-
bustible decorative covering or a piece of .018” mini-
mum sheet metal, to protect hearth extension material.
(Fig. 25)
Secure the hearth extension to the floor to prevent
shifting, using trim molding or other similar means at
three (3) outer edges. Seal crack between the fireplace
hearth and hearth extension with a noncombustible
material. (Figs. 24 and 25)
WARNING: Hearth extension must be installed in
accordance with Figure 24. Top of hearth extension
must be level with bottom of fireplace.
Alternate noncombustible materials may be used
providing the (total) thermal resistance (Rt value) of the
alternate material employed is greater than or equal to
R = 1.09 Thermal resistance (R) or thermal conductivity
(K), may be obtained from manufacturer of the material.
Factors are related by the formula K = 1/R. (Fig. 23)
T = given thickness
R = thermal resistance for a given thickness (T)
K = thermal conductivity
Noncombustible material with a lower R value may
be used, provided thickness of material is sufficiently
greater to maintain an equivalent (total) thermal resis-
tance (Rt).
Example of Determining Hearth Extension
Equivalents
To determine the thickness required for any new mate-
rial:
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required
thickness).
FP1202a
EWF30
SEALING DETAILS
6/05
Wall Covering
2 x 4 Header - Do not
notch at standoffs
Noncombustible
Decorative
Facing
Seal all cracks
between fireplace sur-
round (steel) and wall
materials with noncom-
bustible material.
Cast Front
Noncombustible
Decorative
Covering
Safety Strips - Must be
overlapped 1/2” minimum
FP1202a
Fig. 24 Sealing gaps.
NOTE: No
material
may cover
black cast
face.
COMMON MATERIALS AND FACTORS
MATERIAL K*
R
MINIMUM
THICKNESS
EH2416
Common Brick
0.916
5.0
2.18 1.0 in.**
0.10 5.46 in.**
(CFM Corporation)
R Value is for 1/2 inch.
* Units of K = BTU/SQ FT/HR/˚F/IN
** Thickness of Listed Material
FP533ADD
Addendum
6/1/99 djt
8/4/99 changed .2 to .1
one inch to 1/2 inch djt
FP533ADD
Fig. 23 Hearth extension material factors.
NEW K of new material (per inch) thickness
required = X of listed
thickness K of listed material (per inch) material
Noncombustible
Material