10
1 SQ IN.
PER
4000
BTUH*
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 4000
BTUH*
CIRCULA
TING
AIR DUCTS
VENT
THROUGH
ROOF
D
B
A
C
E
1 SQ IN.
PER 4000
BTUH*
DUCT
TO
OUTDOORS
CIRCULATING AIR DUCTS
1 SQ IN.
PER 2000
BTUH*
1 SQ IN.
PER 2000
BTUH*
DUCTS
TO
OUTDOORS
12
″
MAX
12
″
MAX
12
″
MAX
Use any of the following
combinations of openings:
A & B C & D D & E F & G
NOTE:
*Minimum dimensions of 3 in.
12
″
MAX
12
″
MAX
OUTDOORS
1 SQ IN.
PER
4000
BTUH*
F
G
CLEAR
ANCE IN FRONT
OF COMB
USTION AIR
OPENINGS SHALL BE
AT LEAST 3 IN.
A03174
Fig. 7
---
Air for Combustion, Ventilation, and Dilution for
Outdoors
Table 3--Minimum Space Volumes
were determined by using
the following equations from the National Fuel Gas Code ANSI
Z223.1--2006/NFPA 54--2006,8.3.2.2:
1. For
other than fan--assisted appliances
, such as a draft
hood--equipped water heater:
Volume
Other
= 21ft
3
ACH
I
other
1000 Btu/hr
A04002
2. For
fan--assisted appliances
such as this furnace:
Volume
Fan
= 15ft
3
ACH
I
fan
1000 Btu/hr
A04003
If:
I
other = combined input of all other than
fan--assisted
appliances
in Btuh/hr
I
fan = combined input of all fan--assisted appliances in Btuh/hr
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 closeable doors between rooms.
CIRCULATING AIR
DUCTS
6" MIN
(FRONT)
†
CIRCULATING AIR DUCTS
VENT THROUGH ROOF
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
12" MAX
1 SQ IN.
PER 1000
BTUH* IN DOOR
OR WALL
12" MAX
* Minimum opening size is 100 sq in. with
minimum dimensions of 3 in.
†
Minimum of 3 in. . when type-B1 vent is used.
UNCONFINED
SPACE
INTERIOR
HEATED
SPACE
CLEARANCE IN FRONT OF COMBUSTION AIR
OPENINGS
SHALL
B
E A
T
LEAST 3 IN.
A03175
Fig. 8
---
Air for Combustion, Ventilation, and Dilution From
Indoors
b. Combining spaces on same floor level. Each opening
shall have free area of at least 1 in.
2
/1,000 Btuh (2,000
mm
2
/kW) of the total input rating of all gas appliances
in the space, but not less than 100 in.
2
(0.06 m2). One
opening shall commence within 12 in. (300 mm) of
the ceiling and the second opening shall commence
within 12 in. (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 permanent openings in doors or floors
having free area of at least 2 in.
2
/1,000 Btuh (4,400
mm
2
/kW) of total input rating of 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 out-
doors having free area of at least 1--in.
2
/4,000 Btuh of total
input rating for all gas appliances in the space.
3. In spaces that use the Indoor Combustion Air Method, in-
filtration should be adequate to provide air for combus-
tion, permanent ventilation and dilution of flue gases.
However, in buildings with unusually tight construction,
additional air MUST be provided using the methods de-
scribed in the
Outdoor Combustion Air
Method section.
PG
8J
/M
