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TO
OUTDOORS
1 SQ IN.
PER4000
BTUH*
12"MAX
1 SQ IN.
PER2000
BTUH*
T
DUCTS
TO
OUTDOORS
1 SQ IN.
PER2000
BTUH
T
12"*MAX
12"
MAX
1 SQ IN.
PER
4000
BTUH*
co
o
o
a
S
o
1 SQ IN.
PER
4000
BTUH*
12 "_
MAX
t
CIRCULATING AIR DUCTS
TO
OUTDOORS
*Minimum
dimensions
of 3 in.
NOTE:
Use any of the following
combinations
of openings:
A&B
C&D
D&E
F&G
1SQ IN
PER4000
BTUH*
A03174
Fig. 17--Air
for Combustion,
Ventilation,
and Ditution
for Outdoors
1. Adjoining
rooms
can be considered
part of a space ik
a There
are no closable
doors between
rooms.
b. Combining
spaces
on same floor level
Each opening
shall
have free area of at least 1 in.2/1,000
Bmh (2,000 mm2&W)
of the total input rating
of all gas appliances
in the space,
but not less than
100 in. 2 (0.06
m 2) One opening
shall
commence
within
12" (300 nrm)
of the
ceiling
and the
second
opening
shall commence
within
12" (300 ram)
of
the floor. The mininmm
dimension
of air openings
shall be
at least 3 in. (80 ram). (See Fig. 18.)
c. Combining
space
on dif£)rent
floor
levels. The volumes
of
spaces
on
different
floor
levels
shall
be
considered
as
communicating
spaces
if connected
by one or more permao
nest openings
in doors
or floors having
fi'ee area of at least
2 in.S/l,000
Bmh (4,400
ramS&W)
of total input rating
of
all gas appliances.
2. An attic or crawlspace
*nay be considered
a space
that freely
communicates
wit}* the outdoors
provided
there are adequate
permanent
ventilation
openings
directly
to outdoors
having
fi'ee area of at least
1-in.2/4,000
Bmh
of total input rating
for
all gas appliances
in the space.
3. In spaces
that
use
d_e Indoor
Combustion
Air
Method,
infiltration
should be adequate
to provide
air for combustiom
permanent
ventilation
and diludon
of flue gases. However,
in
buildings
with
unusually
tight
construction,
additional
air
MUST
be
provided
using
the
methods
described
in the
Outdoor
Combustion
Air Method
section.
_
CIRCULATING[
DUCTS
AIR
I
I
VENT THROUGH ROOF
INTERIOR
HEATED
SPACE
-
l
CIRCULATING AIR DUCTS
F-
_ 1 SQ IN.
co
PER 1000
D
ca
BTUH* IN DOOR
:_
ORWALL
O
o
m
UNCONFINED
O
SPACE
k-
Z
o
a:
6" MtN
m
(FRONT)t
z
Ld
o
1 SQtN.
z
PER 1000
<
a:
BTUH* IN DOOR
<:
S ORWALL
LU
o
L12" MAX
* Minimum
opening
size is 100 sq in. with
minimum
dimensions
of 3 in.
'Minimum
of 3 in when type-B1
vent is used
A03175
Fig. 18--Air
for Combustion,
Ventilation,
and Dilution
from Indoors
L nusually
tight construction
is defined
as
( onstr_/ction
with:
a. Walls and ceilings
exposed
to the outdoors
have a continu_
ous, sealed
vapor bare'let.
Openings
are gasketed
or sealed
and
b. Doors
and openable
windows
are weatherstripped
and
c. Other openings
are caulked
or sealed.
These
include
joints
around
window
and door frames,
between
sole plates
and
floors, between
wall-ceiling
joints,
between
wal! panels,
at
penetrations
fbr plumbing,
electrical
and gas lines, etc.
NOTE:
In detem_ining
the fi'ee area of an opening,
the blocking
ef_kct of the louvers,
grilles,
and screens
must be considered.
If the
free
area of a louver
or grille
design
is unknown,
it may
be
assumed
that wood
louvers
have a 20 percent
fi'ee area, and metal
louvers
or grilles
have a 60 percent
fi'ee area. Screens,
when used,
must not be smaller
than 1i4oin. mesh.
Louvers
and grilles must be
constructed
so they cannot
be closed.
When
combustion
air ducts are used,
they nmst
be of the same
cross sectional
area as d-*eflee area of the openings
to which
they
connect.
The minimum
dimension
of ducts must not be less than 3
in. (80mm).
Combination
of Indoor
and
Outdoor
Air
1. [ndoor
openings
shall compy
with
the Indoor
Combustion
Air Method
below
and,
2. Outdoor
openings
shall be located
as required
in the Outdoor
Combustion
Air Method
mentioned
previously
and,
17
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