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CiUTLET
_
AE_
!/ENI
PEPE
INLET
AZR
\/ENTZLATZON
LOUVERS
FOR
UNIIEATED
CRAWL
SPACE
/
I FIGURE 2 1
B. When
communicating
with the outdoors
by
means of vertical ducts, each opening shall have
a minimum
free area I square inch per4,000
BTU
per hour of totat input rating ofatt appliances
in the
enclosed
space.
(Figure
3)
I FIGURE 3 I
C. If horizontal
ducts are used, each opening shall
have
a minimum
free
area
1 square
inch per
2,000
BTU
per
hour
total
input
rating
of all
appliances
in the enclosed
space. (Figure
4)
VE_S
PIPE
\)
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D. When ducts are used, they shall be of the same
cross sectional
area as the free area of the area
of the
openings
to which
they
connect.
The
minimum
dimension
of rectangular
air ducts shall
not be less than 3 inches.
6. In calculating
free area using
louvers,
grills or
screens
for the above, consideration
shall be given
to their blocking
effect.
Screens
used shall not be
smaller than 1/4 inch mesh. If the free area through
a design of louver or grill is known,
it should be used
in calculating
the size opening
required
to provide
the free area specified.
If the design and free area is
not known, it may be assumed
that wood louvers wilt
have 20-25% free area and metal louvers and grills
will have 60-75%
free area. Louvers
and grills shall
be fixed in the open position
or interlocked
with the
boiler so that they are opened
automatically
during
boiler operation.
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