440 01 1024 01
Specifications are subject to change without notice
11
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 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 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.
Table 2
M
INIMUM SPACE VOLUME FOR 100% COMBUSTION AND VENTILATION AIR FROM INDOORS (ft
3
)
Other Than Fan- Assisted Total
(1,000’s Btuh)
Fan- assisted Total
(1,000’s Btuh)
ACH
30
40
50
40
50
60
75
100
125
0.60
1,050
1,400
1,750
1,000
1,250
1,500
1,875
2,500
3,125
0.50
1,260
1,680
2,100
1,200
1,500
1,800
2,250
3,000
3,750
0.40
1,575
2,100
2,625
1,500
1,875
2,250
2,813
3,750
4,688
0.30
2,100
2,800
3,500
2,000
2,500
3,000
3,750
5,000
6,250
0.20
3,150
4,200
5,250
3,000
3,750
4,500
5,625
7,500
9,375
0.10
6,300
8,400
10,500
6,000
7,500
9,000
11,250
15,000
18,750
0.00
NP
NP
NP
NP
NP
NP
NP
NP
NP
NP = Not Permitted
Table 2 Minimum Space Volume
s were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1/NFPA 54--2006, 9.3.2.2:
1.
For
other than fan--assisted appliances
such as a draft
hood--equipped water heater,
1000 Btu / hr
21 ft
3
(
I
other
)
Volume
other
=
ACH
2.
For
fan--assisted appliances
such as this furnace,
1000 Btu / hr
15 ft
3
(
I
fan
)
Volume
fan
=
ACH
If:
I
other
= combined input of all
other than fan--assisted
appliances
in Btu/hr
I
fan
= combined input of all
fan--assisted appliances
in Btu/hr
ACH
= air changes per hour (ACH shall not exceed 0.60).
The following requirements apply to the
Standar
d 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
@
/1,000 BTUH (2,000
mm
@
/kW) of the total input rating of all gas appliances in the
space, but not less than 100 in
@
(0.06 m
@
). One opening shall
commence within 12
″
of the ceiling and the second opening
shall commence within 12
″
of the floor. The minimum
dimension of air openings shall be at least 3
″
.
•
Combining spaces on different floor levels. The volumes of
spaces on different floor levels shall be considered
communicating spaces if connected by one or more
permanent openings in doors or floors having a free area of at
least 2 in
@
/1,000 Btuh (4,400 mm
@
/kW) of total input rating of
all gas appliances.
•
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
remain open and
NOT
have any means of being closed off.
Ventilation openings to outdoors
MUST
be at least 1 square
inch of free area per 4,000 BTUH of total input rating for all gas
appliances in the space.
•
In spaces that use the
Indoor Combustion Air
Method,
infiltration 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
provided 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
continuous, sealed vapor barrier. Openings are gasketed
or sealed and
2. Doors and openable windows are weather stripped and
3. Other openings are caulked or sealed. These include
joints around window and door frames, between sole
plates and floors, between wall--ceiling joints, between
wall panels, at penetrations for plumbing, electrical and
gas lines, etc.