11
where the air infiltration rate is known to be less than 0.40
ACH,
the method in 9.3.2.2 shall be used. The total required volume shall be the sum of the
required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed
through openings not furnished with doors, and through combustion air openings sized and located in accordance with 9.3.2.3, are considered a part of the
required volume.
9.3.2.1* Standard Method.
The minimum required volume shall be 50 ft
3
per 1,000/Btu/hour (4.8m
3
/kW).
9.3.2.2* Known Air Infiltration Rate Method.
Where the air infiltration rate of a structure is known, the minimum required volume shall be determined
as follows:
(1) For appliances other than fan-assisted, calculate using the following equation:
21 ft
3
I
other
Required Volume
other
> ________
_________
ACH
1000 Btu/hr
(2) For fan-assisted appliances, calculate using the following equation:
15 ft
3
I
fan
Required Volume
fan
> ________
_________
ACH
1000 Btu/hr
where:
I
other
=
all appliances other than fan-assisted input in Btu per hour
I
fan
=
fan-assisted appliances input in Btu per hour
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 in 9.3.2.2(1) and 9.3.2.2(2).
9.3.2.3 Indoor Opening Size and Location.
Openings used to connect indoor spaces shall be sized and located in accordance with the following:
(1)*
Combining spaces on the same story.
Each opening shall have a minimum free area of 1 in.
2
/1000Btu/hr (2200 mm
2
/kW) of the total input rating of
all appliances in the space but not less than 100 in.
2
(0.60m
2
). One opening shall commence within 12 in. (300 mm) of the top, and one opening shall
commence within 12 in. (300 mm) of the bottom, of the enclosure
[see
Figure A.9.3.2.3(1)].
The minimum dimension of air openings shall be not
less than 3 in. (80 mm).
(2)
Combining spaces in different stories
.
The volumes of spaces in different
stories shall be considered as communicating spaces where such spaces are
connected by one or more openings in doors or floors having a total mini-
mum free area of 2 in.
2
/1000 Btu/hr (4400 mm
2
/kW) of total input rating of
all appliances.
9.3.3 Outdoor Combustion Air.
Outdoor combustion air shall be provided
through opening(s) to the outdoors in accordance with the methods in 9.3.3.1
or 9.3.3.2. The minimum dimension of air openings shall not be less than 3 in.
(80 mm).
9.3.3.1 Two Permanent Openings Method.
Two permanent openings, one
commencing within 12 in. (300 mm) of the top and one commencing within 12
in. (300 mm) of the bottom, of the enclosure shall be provided. The openings
shall communicate directly, or by ducts, with the outdoors or spaces that freely
communicate with the outdoors, as follows:
Figure A.9.2.3.3.(1) All Combustion Air from Adjacent
Indoor Spaces through Indoor Combustion Air Openings.
)
(
)
(