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(2) Combining spaces in different stories. The volumes of spaces in dif-
ferent 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.
input rating of all appliances.
9.3.3 Outdoor Combustion Air. Outdoor combustion air shall be pro-
vided 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:
(1)* Where directly communicating with the outdoors or where communi-
cating to the outdoors through vertical ducts, each opening shall have a
minimum free area of 1 in.
rating of all appliances in the enclosure. [See Figure A.9.3.3.1(1)(a)
and Figure A.9.3.3.1(1)(b).]
Figure A.9.3.3.1(1)(a) All Combustion Air From Outdoors -
Inlet Air from Ventilated Crawl Space and Outlet Air to Ventilated
12
2
2
/1000 Btu/hr (4400 mm
2
2
/4000 Btu/hr (550 min
/kW) of total input
Attic.
/kW) of total
(2)*Where communicating with the outdoors through horizontal ducts,
each opening shall have a minimum free area of 1 in.
(1100 min
[See Figure A.9.3.3.1(2).]
Figure A.9.3.3.1(2) All Combustion Air From Outdoors
9.3.3.2* One Permanent Opening Method. One permanent openings,
commencing within 12 in. (300 mm) of the top of the enclosure, shall be
provided. The appliance shall have clearances of at least 1 in. (25 mm) from
the sides and back and 6 in. (150 mm) from the front of the appliance. The
opening shall directly communicate with the outdoors or shall communicate
through a vertical or horizontal duct to the outdoors or spaces that freely
communicate with the outdoors (see Figure A.9.3.3.2) and shall have a
minimum free area of the following:
2
(1) 1 in.
/3000 Btu/hr (700 mm
appliances located in the enclosure, and
(2) Not less than the sum of the areas of all vent connectors in the space.
Figure A.9.3.3.1(1)(b) All Combustion Air
From Outdoors through Ventilated Attic.
2
/kW) of total input rating of all appliances in the enclosure.
through Horizontal Ducts.
2
per kW) of the total input rating of all
2
/2000 Btu/hr
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