9
1 SQ IN.
PER
4000
BTUH*
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 4000
BTUH*
CIRCULATING
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
CLEARANCE IN FRONT
OF COMBUSTION AIR
OPENINGS SHALL BE
AT LEAST 3 IN.
A03174
Fig. 7 -- Air for Combustion, Ventilation, and Dilution for
Outdoors
S Spaces having at least 50 cubic feet per 1,000 Btuh
may use the INDOOR COMBUSTION AIR,
STANDARD or KNOWN AIR INFILTRATION
METHOD.
Outdoor Combustion Air
Method
1. Provide the space with sufficient air for proper
combustion, ventilation, and dilution of flue gases using
permanent horizontal or vertical duct(s) or opening(s)
directly communicating with the outdoors or spaces that
freely communicate with the outdoors.
2. Fig. 7 illustrates how to provide TWO OUTDOOR
OPENINGS, one inlet and one outlet combustion and
ventilation air opening, to the outdoors.
a. One opening MUST commence within 12 in. (300
mm) of the ceiling and the second opening MUST
commence within 12 in. (300 mm) of the floor.
b. Size openings and ducts per Fig. 7 and Table 2.
c. TWO HORIZONTAL DUCTS require 1 square inch
of free area per 2,000 Btuh (1,100 mm2/kW) of
combined input for all gas appliances in the space per
Fig. 7 and Table 2.
d. TWO OPENINGS OR VERTICAL DUCTS require 1
square inch of free area per 4,000 Btuh (550
mm2/kW) for combined input of all gas appliances in
the space per Fig. 7 and Table 2.
3. ONE OUTDOOR OPENING requires:
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 t
e-B1 vent is used.
UNCONFINED
SPACE
INTERIOR
HEATED
SPACE
CLEARANCE IN FRONT OF COMBUSTION AIR
OPENINGS SHALL BE AT LEAST 3 IN.
A03175
Fig. 8 -- Air for Combustion, Ventilation, and Dilution from
Indoors
a. 1 square inch of free area per 3,000 Btuh (734
mm2/kW) for combined input of all gas appliances in
the space per Table 2 and
b. Not less than the sum of the areas of all vent
connectors in the space.
The opening shall commence within 12 in. (300 mm) of the
ceiling. Appliances in the space shall have clearances of at least 1
in. (25 mm) from the sides and back and 6 in. (150 mm) from the
front. The opening shall directly communicate with the outdoors
or shall communicate through a vertical or horizontal duct to the
outdoors or spaces (crawl or attic) that freely communicate with
the outdoors.
Indoor Combustion AirE NFPA & AGA
Standard and Known--Air--Infiltration Rate Methods
Indoor air is permitted for combustion, ventilation, and dilution,
if the Standard or Known--Air--Infiltration Method is used.
315A
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