441 01 2314 06
Specifications are subject to change without notice.
8
Indoor Combustion Air
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in
personal injury or death.
Most homes will require additional air from
outdoors for combustion and ventilation. A space
with at least 50 cubic feet per 1,000 BTUH (4.8 cubic
meters per kW) input rating or homes with tight
construction may need outdoor air, supplied
through ducts, to supplement air infiltration for
proper combustion and ventilation of flue gases.
WARNING
Standard and Known-Air-Infiltration Rate Methods
NFPA & AGA
Indoor air is permitted for combustion and ventilation, if the Stan-
dard or Known−Air−Infiltration Rate Method is used.
The Standard Method may be used, if the space has no less vol-
ume than 50 cubic feet per 1,000 BTUH (4.8 cubic meters per kW)
input rating for all gas appliances installed in the space. The stan-
dard method permits indoor air to be used for combustion and ven-
tilation air.
The Known Air Infiltration Rate Method shall be used if the in-
filtration rate is known to be less than 0.40 air changes per hour
(ACH) and 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 2 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 vol-
ume for the space.
Table 2
MINIMUM SPACE VOLUME FOR 100% COMBUSTION AND VENTILATION AIR FROM INDOORS
Other Than Fan-Assisted Total Fan-assisted Total
ACH
30,000 BTU
(8.79 kW)
40,000 BTU
(11.72 kW)
50,000 BTU
(14.65 kW)
50,000 BTU
(14.65 kW)
75,000
(21.98 kW)
100,000 BTU
(29.30 kW)
125,000 BTU
(36.63 kW)
150,000 BTU
(43.95 kW)
ft
3
(m
3
)
0.60 1,050 (29.7) 1,400 (39.2) 1,750 (49) 1,250 (35) 1,875 (52.5) 2,500 (70) 3,125 (87.5) 3,750 (105)
0.50 1,260 (35.3) 1,680 (47.04) 2,100 (58.8) 1,500 (42) 2,250 (63) 3,000 (84) 3,750 (105) 4,500 (126)
0.40 1,575 (44.1) 2,100 (58.8) 2,625 (73.5) 1,875 (52.5) 2,813 (78.8) 3,750 (105) 4,688 (131.3) 5,625 (158)
0.30 2,100 (58.8) 2,800 (78.4) 3,500 (98) 2,500 (70) 3,750 (105) 5,000 (140) 6,250 (175) 7,500 (210.6)
0.20 3,150 (88.2) 4,200 (117.6) 5,250 (147) 3,750 (105) 5,625 (157.5) 7,500 (210) 9,375 (262.5) 11,250 (316)
0.10 6,300 (176.4) 8,400 (235.2) 10,500 (294) 7,500 (210) 11,250 (315) 15,000 (420) 18,750 (525) 22,500 (632)
0.00 NP NP NP NP NP NP NP NP
NP = Not Permitted
Table 2 Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1/NFPA 54−2009, 9.3.3.2:
1. For other than fan−assisted appliances such as a draft
hood−equipped water heater,
1000
BTUH
21 ft
3
(
I
other
)
Volume
other
=
ACH
.293
kW
59 m
3
(
I
other
)
Required
Volume
other
ACH
2. For fan−assisted appliances such as this furnace,
If:
I
other
= combined input of all other than fan−assisted
appliances in BTUH
I
fan
= combined input of all fan−assisted appliances in
BTUH
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.
• Adjoining rooms can be considered part of a space, if there
are no closable doors between rooms.
• Combining spaces on the same floor level. Each opening
shall have a free area of at least 1 in.
2
/1,000 BTUH (22
cm
2
/kW) of the total input rating of all gas appliances in the
space, but not less than 100 in.
2
(645 cm
2
). Once opening
shall commence within 12” (604.8mm) of the ceiling and the
second opening shall commence within 12” (604.8mm) of the
floor. The minimum dimension of air openings shall be at least
3 in(76.2mm).
• An attic or crawl space may be considered a space that freely
communicates with the outdoors provided there are adequate
ventilation openings directly to outdoors. Openings MUST re-
main open and NOT have any means of being closed off. Ven-
tilation openings to outdoors MUST be at least 1 square inch
of free area per 4,000 BTUH (5.5 cm
2
/kW) of total input rating
for all gas appliances in the space.
• In spaces that use the Indoor Combustion Air Method, in-
filtration should be adequate to provide air for combustion,
ventilation and dilution of flue gases. However, in buildings
with unusually tight construction, additional air MUST be pro-
vided using the methods described in section titled Outdoor
Combustion Air Method:
• Unusually tight construction is defined as Construction with:
1. Walls and ceilings exposed to the outdoors have a continu-
ous, sealed vapor barrier. Openings are gasketed or
sealed and
2. Doors and openable windows are weather stripped and
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