N.Y.C. Admin. Code § 27-756: § 27-756 Installation and operation of ventilating and air conditioning systems.

Where mechanical ventilation is accepted as an alternate for, or a supplement to, natural means of ventilation, or is required under the conditions herein prescribed, or where ventilation is provided by means of air conditioning system, the system, equipment, and distributing ducts shall be installed in accordance with the applicable provisions of subchapters thirteen through fifteen of this chapter. Such required ventilating and/or air conditioning systems shall be kept in operation at all times when the building or space is being used in a normal manner in accordance with the purpose for which it was intended.