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APPENDIX
A:
HEARTH PROTECTOR REQUIREMENTS
How much floor protection do I need?
The Harman Oakwood has been tested
to
require
e
a k-value
of
.84 which is equal
to
typical .75" mill board.
Check with mill board manufacturer
for
exact density.
It
is required that
you
have a hearth
pad
under
your
Oakwood
that will protect your flooring from heat and burn-
ing. To determine
the
thickness
of
your
hearth material
you
will need
to
take into consideration the thermal conductivity, or
(k) value
of
your
stove. K value can
be
calculated
by
knowing
the amoung
ofBTD's
(British Thermal
Units)
that will flow
in
one
hour
through one square foot
of
a layer one inch
thick
of
a
uniform material
per
Farenheit degree differenc:e
between
op-
posite surfaces
of
the layer.
(BTU) (inch)
Example: A piece
of
2 inch
thick
hearth material specified for
use
by
a manufacturer has a k value
of
.84.
If
the temperature
on
the
side
exposed
to
the
radiant front
of
the fireplace is 100°
F higher than the side exposed
tot
he
floor,
each
square foot
of
the heart protector will transfer
42
BTUs
through
to
the
com-
bustible materials beneath
it
during
each
hour
of
operation.
Using the above formula, the calculation for
the
heat
transfer
would
be
done as follows:
.84
BTU
-
inch
x
~.
x 1 s9·
f
t.
x
lOO°F
=
42
BTU
sq. ft. -
hr
-
OF
2 mches
It follows from this example that
if
1
inch
of
a certain material
transfers
84
BTUIhr under these conditions,
then
2 inches will
transfer
112
that amount (i.e.
42
BTUIhr), 3 inches will trans-
fer 1/3 that amount,
and
so on.
NOTE:
The
hearth
extension protection materials
that
are
specified
by
most manufacturers are
much
better insulators
than most common masonry materials.
Common
masonry must
often
be
many
times thicker
than
special materials
recom-
mended.
What
thickness do I need
if
I
am
using a different mate-
rial
other
than
those specified
by
the manufacturer?
If
a manufacturer's specifications call for a material
having a
minimum
thickness
of
1 inch with a certain k value,
any material substituted for that specified material
must
have
the same thickness and
have
the same
or
lower
k value,
or
if
the k value
of
the selected alternate material
in
higher, a greater
thickness
of
that material must
be
used.
In
some cases,
if
the
k value is lower, thinner materials
may
be
used. The following
formula gives the means
of
determining thickness
of
alternate
materials.
k
of
the alt. material
x thickness of
specified
material
= thickness of
alt.
material
k of the specified material
30 Oakwood Wood Stove
Example:
The
manufacturer
specifies
a certain
material
a
mini-
mum of· 1 inch thick that is appropriate for use
as
a hearth
extension
with
their
fireplace
system.
The
k
value
for
that
ma-
terial
is
.84.
You
decide to
use
common
brick
for
hearth
exten-
sion protection instead
of
that specified material. How thick
must the common brick hearth extension be to be equivalent
with that which the manufacturer specifies? Common brick
has
a k
value
of
5.
Using the given formula to determine
the
equivalent
thickness
of
common brick
for
the
hearth extension, you will
divide
5 by
.84,
which
gives
a
thickness
of
5.95
inches
of
com-
mon brick This means that it would take about
siX
inches of
brick
to
provide
the
same
thermal
protection
as
one
inch
of
the
specified material.
EXample
2:
In
example
1,
the
specified
k
value
for
a
minimum
of 1 inch thick hearth extension material is
.84.
Suppose you
hae a non-combustible material that comes in
3/8
inch
sheets.
Its k
value
is.55.
What
is
the
minimum
thickness
of
this
material
needed to
be
equivalent or better than that specified by the
manufacturer?
Using the given formula
.55
x 1 =
.65
inches (thickness for
equivalent .84protection)
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