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16
Vermont Castings EWF36A
20005167
Examples of wall shield insulation:
1. Manville - CERAFORM 126, K=.27,
1/2 inches thick
2. EH2416, K = .458,
1 inch thick required.
Hearth Installation
A hearth extension is required to protect a combustible
floor in front of the fireplace. Refer to Figure 26 for mini-
mum dimensions and mounting detail.
NOTE: Hearth Extension must not cover the air
inlet opening of a fireplace.
The hearth extension described in Figure 26 must be a
durable noncombustible material with a minimum (total)
Rt value of 1.09; refer to Figure 24 for examples. The
overall height (above a combustible floor), depth and
width must be as indicated, with the extension centered
to the fireplace opening.
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. 26)
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. 25 and 26)
WARNING: Hearth extension must be installed in
accordance with Figure 25. 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. 24)
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:
FP550
BR/BC - SEALING
DETAILS
9/29/97
Wall Covering
2 x 4 Header - Do not
notch at standoffs
Noncombus-
tible Decorative
Facing
Seal all cracks
between fireplace sur-
round (steel) and wall
materials with noncom-
bustible material.
Cast Front
Noncombustible
Decorative Cover-
ing
Safety Strips - Must be
overlapped 1/2” minimum
FP1202
Fig. 25 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. 24 Hearth extension material factors.
NEW K of new material (per inch) thickness
required = X of listed
thickness K of listed material (per inch) material
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required
thickness).