TO
OUTDOORS
1SQ IN.
PER4000
BTUH*
12"MAX
1SQ IN.
PER2000
BTUH*
T
DUCTS
TO
OUTDOORS
1SQ IN.
PER2000
BTUH T
12"*MAX
12"
MAX
1SQ IN.
PER
4000
BTUH*
co
o
o
a
S
o
1SQ 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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