Installation Guide

12
(1)*Where directly communicating with the outdoors or where communicating to the outdoors through vertical ducts, each opening shall have a minimum
free area of 1 in.
2
/4000 Btu/hr (550 min
2
/kW) of total input 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).]
(2)*Where communicating with the outdoors through horizontal ducts, each
opening shall have a minimum free area of 1 in.
2
/2000 Btu/hr (1100 min
2
/
kW) of total input rating of all appliances in the enclosure. [See Figure
A.9.3.3.1(2).]
9.3.3.2* One Permanent Opening Method. One permanent openings, com-
mencing 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 hori-
zontal 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:
(1) 1 in.
2
/3000 Btu/hr (700 mm
2
per kW) of the total input rating of all 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.
Figure A.9.3.3.1(1)(a) All Combustion Air From Outdoors -
Inlet Air from Ventilated Crawl Space and Outlet Air to Ventilated Attic.
Figure A.9.3.3.1(2) All Combustion Air From Outdoors
through Horizontal Ducts.
Figure A.9.3.3.2 All Combustion Air
From Outdoors through Single Combustion Air Opening.