Air inlets shall lead to the outer air and open at a convenient point, on the footway in the front of the building or at the curb line, and shall have a cover with openings at least three-fourths of the area of the pipe. In no case shall an air inlet open within 10 feet of any door, window, or fresh air intake for a heater or ventilation system.
They shall be so arranged as to prevent the admission of sticks or other articles that would tend to obstruct the main trap. They shall be at least 1/4 inch in thickness and fastened with brass screws or bolts in order that the top can be removed if necessary, and the body shall be caulked fast to the upright pipe by a lead joint. Only approved air inlets shall be used.