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9.3.2 Indoor Combustion Air. The required volume of indoor air shall be determined in accordance with the method in 9.3.2.1 or 9.3.2.2 except that
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
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:
Required Volume
> ________ _________
other
(2) For fan-assisted appliances, calculate using the following equation:
Required Volume
> ________ _________
fan
where:
I
=
all appliances other than fan-assisted input in Btu per hour
other
I
=
fan-assisted appliances input in Btu per hour
fan
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
all appliances in the space but not less than 100 in.
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 open-
ings 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
minimum free area of 2 in.
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:
(
3
)
21 ft
I
other
ACH
1000 Btu/hr
15 ft
3
(
I
)
fan
ACH
1000 Btu/hr
2
/kW) of the total input rating of
2
2
2
/1000 Btu/hr (4400 mm
/kW) of total input
3
per 1,000/Btu/hour (4.8m
2
(0.60m
). One
Figure A.9.2.3.3.(1) All Combustion Air from Adjacent
Indoor Spaces through Indoor Combustion Air Openings.
3
/kW).
11
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