12
440 01 1051 02
Specifications are subject to change without notice.
Indoor Combustion Air (Unconfined Space)
!
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
Standard
or
Known
−
Air
−
Infiltration Rate
Method is used.
The
Standard
Method may be used, if the space has no less
volume 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
standard
method permits indoor air to be used for combustion and
ventilation air.
The
Known Air Infiltration Rate
Method shall be used if the
infiltration 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
volume for the space.
CARBON MONOXIDE POISONING HAZARD
Failure to supply additional air by means of
ventilation grilles or ducts could result in personal
injury or death.
An unconfined space or homes with tight
construction may not have adequate air infiltration
for proper combustion and ventilation of flue gases.
Most homes will require additional air.
!
WARNING
Table 2
M
INIMUM SPACE VOLUME FOR 100% COMBUSTION AND VENTILATION AIR FROM INDOORS
Other Than Fan-Assisted Total
Fan-assisted Total
ACH
30,000 BTU
(8,790 kW)
40,000 BTU
(11,720 kW)
50,000 BTU
(14,650 kW)
50,000 BTU
(14,650 kW)
75,000
(21,975 kW)
100,000 BTU
(29,300 kW)
125,000 BTU
(36,625 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)
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)
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)
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)
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)
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)
0.00
NP
NP
NP
NP
NP
NP
NP
ACH = Air Changes per Hour
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, 9.3.2.2:
1.
For
appliances
other than fan
−
assisted appliances
(such
as a draft hood
−
equipped water heater), calculate using the
following equation:
1000 BTUH
21 ft
3
(
I
other
)
Required Volume other
ACH
.293 kW
59 m
3
(
I
other
)
Required Volume other
ACH
2.
For
fan
−
assisted appliances
(such as this furnace),
calculate using the following equation:
1000 BTUH
15 ft
3
(
I
fan
)
Required Volume fan
ACH
.293 kW
.42 m
3
(
I
fan
)
Required Volume fan
ACH
where:
I
other
= all appliances
other than fan
−
assisted
input in BTUH
I
fan
=
fan
−
assisted appliance
input in BTUH
ACH
= air change per hour (percent of volume of space
exchanged per hour, expressed as a decimal)
3.
For purposes of this calculation, an infiltration rate greater
than 0.60 ACH shall not be used in the equations above.
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 story. Each opening shall
have a minimum free area of at least 1 in.
2
/1,000 BTUH (22
cm
2
/kW) of the total input rating of all appliances in the space
but not less than 100 in.
2
(645 cm
2
). One opening shall
commence within 12 in. (304.8 mm) of the top, and one
opening shall commence within 12 in. (304.8 mm)of the
bottom, of the enclosure. The minimum dimension of air
openings shall not be less than 3 in (76.2 mm).
•
Combining spaces in different stories. The volumes of spaces
on different stories shall be considered as communicating
spaces where such spaces are connected by one or more
