Section 8: Finishing; Hearth Extension; Alternate Floor Protection Worksheet - Heatilator CONSTITUTION C-40 Owner's Manual

8
Finishing
A. Hearth Extension
A hearth extension must be installed with all fireplaces to
protect the combustible floor in front of the fireplace from
both radiant heat and sparks. See Figures 38.1 below, and
Figures 40.1 and 40.2 on page 40.
Hi g h temperature
(300°F min.) continuous,
non-combustible sealant
HX3 or HX4
Hearth Ext
Tile, stone or other
or equivalent
non-combustible material
insulation
(see Table below)
Floor constructed of wood or
o th e r co m bus ti b l e m a t e ri a l
Figure 38.1 Hearth Extension Construction
WARNING
Fire Risk
• Maintain clearances.
• Use only non-combustible material below
standoffs, material such as cement board
is acceptable.
• Framing or finishing material used on the front
of, or in front of, the appliance closer than the
minimums listed, must be constructed entirely of
noncombustible materials (i.e., steel studs, concrete
board, etc.).
B. Calculating Alternate Floor Protection
Material
Thermal Conductivity: k value
The k value indicates the amount of heat (in BTU's) that will flow
in 1 hour through 1 square foot of a uniform material 1 inch thick
for each degree (F) of temperature difference from one side of
the material to the other. The LOWER the k factor means less
heat is being conducted through the non-combustible material
to the combustible material beneath it. The k value of a mate-
rial must be equal or smaller then the required k value to be
acceptable.
(BTU) (inch)
(foot (hour) (
2
Thermal Resistance: R value
The R value is a measure of a material's resistance to
heat transfer. R value is convenient when more than one
material is used since you can add the R values together,
Page 38
Protective
Metal Hearth
Strip
2 in. (51 mm)
required
o F)
Heatilator • Constitution EPA Fireplace • 480-1091C
whereas you can not do this for k value. The HIGHER the R
factor means less heat is being conducted through the non-
combustible material to the combustible material beneath it.
The R value of a material must be equal or larger then the
required R value to be acceptable.
Converting k to R:
Divide 1 by k and multiply the results times the thickness in inch-
es of the material.
R = 1/k x inches of thickness
Converting R to k:
Divide the inches of thickness by R.
k = inches of thickness/R
Calculations:
Example: Floor protection requires k value of 0.84 and 3/4 inch
thick.
Alternative material has a k value of 0.6 and is 3/4 inch thick.
Divide 0.6 by .75 = k value of 0.80. This k value is smaller than
0.84 and therefore is acceptable.
Table 38.2
Hearth Extension Insulation Alternatives
Minimum R Value = 2.18
Material
Hearth & Home HX3, HX4
USG Micore 300™
USG Durock™ Cement Board
Cement Mortor
Common Brick
Ceramic Tile
Armstrong™ Privacy
Guard Plus
Marble
Minimum
k per inch R per inch thickness
thick thick required
0.49 2.18
0.49 2.18
1.92 0.52 2-1/4 in.
5.0 0.20 5-7/8 in.
5.0 0.20 5-7/8 in.
12.50 0.08 14-5/8 in.
0.46 2.18
14.3-20.0 0.07-0.05 16-5/8 in. - 23-3/8 in.
November 11, 2008
1 in.
1 in.
1/2 in.