18-28-703.3 Outdoor air.

   All air from outdoors. The confined space shall communicate with the outdoors in accordance with methods 1 or 2, which follow. The minimum dimension of air openings shall be not less than 3 in. (80 mm). If ducts are used, the ducts shall be of the same cross- sectional area as the free area of the openings to which they connect.

   1.   Two permanent openings, one commencing within 12 in. (300 mm) of the top of the enclosure 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 with attic spaces that freely communicate with the outdoors.

      (a)   If directly communicating with the outdoors or if communicating to the outdoors through vertical ducts, each opening shall have a minimum free area of 1 in.2 per 4000 Btu/hr (550 mm 2/kW) of the total input rating of all equipment in the enclosure.

      (b)   If communicating with the outdoors through horizontal ducts, such opening shall have a minimum free area of not less than 1 in.2 per 2000 Btu/hr (1100 mm 2 /kW) of the total input rating of all equipment in the enclosure.

   2.   One permanent opening commencing within 12 in. (300 mm) of the top of the enclosure, shall be permitted if the equipment has clearances of at least 1 in. (25 mm) from the sides and back and 6 in. (160 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or shall communicate with the outdoors through a vertical or horizontal duct or space that freely communicate with the outdoors. The opening shall have a minimum free area as follows:

      (a)   1 in.2/3000 Btu/hr (700 mm 2 per kW) of the total input rating of all equipment located in the enclosure, and

      (b)   Not less than the sum of the areas of all vent connectors in the confined spaces.

18-28-704 Deliberately Omitted.

18-28-705 Engineered Installations.

18-28-705.1

   Engineered combustion air installations shall provide an adequate supply of combustion and dilution air and shall be approved by the authority having jurisdiction.

18-28-706 Forced Combustion Air Supply.

18-28-706.1 Mechanical combustion air supply for oil-fired appliances.

   Where all combustion air and dilution air is provided by a mechanical forced-air system, the combustion air and dilution air shall be supplied at the minimum rate of 1 cfm per 2,400 Btu/h [0.00067 m 3 /(s x kW)] of combined input rating of all the fuel-burning appliances served. Each of the appliances served shall be electrically interlocked to the mechanical forced-air system so as to prevent operation of the appliances when the mechanical system is not in operation. Where combustion air and dilution air is provided by the building's mechanical ventilation system, the system shall provide the specified combustion/dilution air rate in addition to the required ventilation air.

18-28-706.2 Mechanical combustion air supply for gas-fired appliances.

   Where all combustion air is provided by a mechanical air supply system, the combustion air shall be supplied from outdoors at the minimum rate of 0.35 ft 3 /min per 1,000 Btu/hr (0.034 3/mm per kW) for all appliances located within the space.