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WARNING: Hearth extension must be installed in
accordance with Figure 23 and must not cover the
bottom front opening of the circulating model.
Alternate noncombustible materials may be used pro-
viding the (total) thermal resistance (Rt value) of the al-
ternate 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).
COMMON MATERIALS AND FACTORS
MATERIAL
EH2416
0.458
(MHSC)
Common Brick
5.0
R Value is for 1/2 inch.
* Units of K = BTU/SQ FT/HR/˚F/IN
** Thickness of Listed Material
Fig. 22 Hearth extension material factors.
Example of Determining Hearth Extension
FP533ADD
Addendum
Equivalents
6/1/99 djt
To determine the thickness required for any new mate-
8/4/99 changed .2 to .1
one inch to 1/2 inch djt
rial:
NEW
K of new material (per inch)
required
= --------------------------------------- X
thickness
K of listed material (per inch)
Example for Common Brick
T (new) = 5.0/0.458 x 0.50 in. = 5.46 in. (new required
thickness).
7412647
MINIMUM
K*
R
THICKNESS
1.09
0.50 in.**
0.10
5.46 in.**
FP533ADD
thickness
of listed
material
BFC36 Balanced Flue Heat-Circulating Fireplace
Wall Covering
Noncombustible
Decorative Fac-
ing
Seal all cracks
between fireplace
surround and wall
materials with non-
combustible material.
Noncombus-
tible Decorative
Covering
Hearth Exten-
sion Insulation
FP550
Fig. 23 Sealing gaps.
Glass Door Operation
The BFC36 is intended for use only with the doors fully
closed. (Fig. 28)
Correct
Fig. 28 Correct door position.
Side View
2 x 4" Header
- Do not notch at
standoffs
Seal crack between
fireplace and hearth
extension with noncom-
bustible material
Safety Strips -
Must be overlapped 1/2"
minimum
FP550
BR/BC - SEALING
DETAILS
9/29/97
Wrong
KT108b
KT108b
BFC
Correct door position
8/23/00 djt
17
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