Indoor Combustion Air ° NFPA & AGA
Standard and Known-Air-Infiltration Rate
Methods
Indoor combustion air is permitted for combustion, ventilation,
and dilution, if the Standard or Known-Air-Infiltration Rate
Method is used.
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal
injury or death.
Many homes require air to be supplied from outdoors
for furnace combustion, ventilation, and dilution of flue
gases.
The furnace combustion air supply must be provided in
accordance with this instruction manual.
Figure 6
Air for Combustion, Ventilation,
and Dilution for Outdoors
A'_ 1 SQ IN.
DUCTS ,
TO _ / _ PER4000
OUTDOORS
._kll_ ......... ........
1
, V
(305r_n_)12"MAX]j
I SQIN. _,1ii
PER2000 IIB
BTUH* J
so i .
PER 2000 A
BTOH*
(305mm) 12"MAXJ | [,
I
l
12" MAX
(305ram)
12_X (305mrn)
1 SO IN.
PER
4000
BTUH*
n-
O
O
£
o
SO IN,
PER
4000
BTUH*
_2j_X (305ram)
t
CIRCULATING AIR DUCTS
I SQ IN,
TO PER 4000
OUTDOORS BTUH*
*Minimum dimensions of 3-in. (76mm)
NOTE: Use any of the following combinations of openings:
A&B, C&D, D&E, F&G
Lt2F012
The Standard Method:
1. The space has no less volume than 50 cubic feet per
1,000 Btuh (4.8 cubic meters per kW) of the maximum
input ratings for all gas appliances installed in the space
and
2. The air infiltrationrate is not known to be less than 0.40
air changes per hour (ACH).
The Known Air Infiltration Rate Method shall be used, if the
infiltration rate is known to be:
1. Less than 0.40 ACH and
2. 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 4 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 4 - 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 other than fan-assisted appliances, such as a
draft hood-equipped water heater
Volume _ 21ft 3 (" I other "_ A04002
Other ACH _.000 Btu/hr]
2. For fan-assisted appliances such as this furnace:
( ) o40o
_ 15ft3 I fan
VolumeFan ACH 000 Btu/hr
If:
Iother=combined input of all other than fan-assisted
appliances in Btuh/hr
Ifan=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 closable doors between rooms.
b. Combining spaces on same floor level. Each opening
shall have free area of at least 1-in.2/1,000 Btuh
(2,000 mm2/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 Figure 7)
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 mm2/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
outdoors 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,
infiltration should be adequate to provide air for
combustion, permanent ventilation and dilution of flue
gases. However, in buildings with unusually tight
construction, additional air MUST be provided using
the methods described in the Outdoor Combustion Air
Method section.
4. Unusually tight construction is defined as Construction
with:
a. Walls and ceilings exposed to the outdoors have a
continuous, sealed vapor barrier. Openings are
gasketed or sealed and
b. Doors and openable windows are weatherstripped
and
c. Other openings are caulked or sealed. These include
joints around window and door frames, between sole
plates and floors, between walt-ceiling joints, between
wall panels, at penetrations for plumbing, electrical
and gas lines, etc.
10 Specificationssubjectto change without notice. 440 01 4001 04
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