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DUCTS
TO
OUTDOORS
12" MAX
1 SQ IN.
PER 2000
B
BTUH*
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 2000
A
BTUH*
12" MAX
CIRCULATING AIR DUCTS
*Minimum dimensions of 3 in.
NOTE:
Use any of the following
combinations of openings:
A & B
C & D
D & E
Fig. 7—Air for Combustion, Ventilation, and
Dilution for Outdoors
The Known Air Infiltration Rate Method shall be used, if the
infiltration rate is known to be:
1. Less than 0.40 ACH and
2. Equal to or greater than 0.10 ACH
Infiltration rates greater than 0.60 ACH shall not be used. The
minimum required volume of the space varies with the number of
ACH and shall be determined per Table 3 or Equations 1 and 2.
Determine the minimum required volume for each appliance in the
space and add the volumes together to get the total minimum
required volume for the space.
Table 3-Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1-2002/NFPA 54-2002,8.3.2.2:
1. For other than fan-assisted appliances, such as a draft
hood-equipped water heater:
= 21ft
Volume
ACH
Other
2. For fan-assisted appliances such as this furnace:
= 15ft
Volume
Fan
1 SQ IN.
PER 4000
BTUH*
D
12"
MAX
VENT
THROUGH
F
ROOF
1 SQ IN.
PER
4000
BTUH*
1 SQ IN.
PER
4000
BTUH*
E
G
12"
MAX
C
12" MAX
DUCT
1 SQ IN.
TO
PER 4000
OUTDOORS
BTUH*
F & G
A03174
I
3
other
1000 Btu/hr
A04002
I
3
fan
ACH
1000 Btu/hr
A04003
CIRCULATING AIR
DUCTS
INTERIOR
HEATED
SPACE
CIRCULATING AIR DUCTS
* Minimum opening size is 100 sq in. with
minimum dimensions of 3 in.
†
Minimum of 3 in . . when type-B1 vent is used.
Fig. 8—Air for Combustion, Ventilation, and
Dilution from Indoors
If:
I
= combined input of all other than fan-assisted appli-
other
ances in Btu/hr
I
= combined input of all fan-assisted appliances in Btu/hr
fan
ACH = air changes per hour (ACH shall not exceed 0.60.)
The following requirements apply to the Standard Method and to
the Known Air Infiltration Rate Method.
1. Adjoining rooms can be considered part of a space if:
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.
of the total input rating of all gas appliances in the space,
but not less than 100 in.
commence within 12" (300 mm) of the ceiling and the
second opening shall commence within 12" (300 mm) of
the floor. The minimum dimension of air openings shall be
at least 3 in. (80 mm). (See Fig. 8.)
c. Combining space on different floor levels. The volumes of
spaces on different floor levels shall be considered as
communicating spaces if connected by one or more perma-
nent openings in doors or floors having free area of at least
2
2 in.
/1,000 Btuh (4,400 mm
all gas appliances.
2. An attic or crawlspace may be considered a space that freely
communicates with the outdoors provided there are adequate
permanent ventilation openings directly to outdoors having
9
VENT THROUGH ROOF
12" MAX
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
UNCONFINED
SPACE
6" MIN
(FRONT)
†
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
12" MAX
A03175
2
2
/1,000 Btuh (2,000 mm
/kW)
2
2
(0.06 m
). One opening shall
2
/kW) of total input rating of
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