N.Y.C. Admin. Code § 27-2031: § 27-2031 Supply of hot water; when required.

Except as otherwise provided in this article, every bath, shower, washbasin and sink in any dwelling unit in a multiple dwelling or tenant-occupied one-family or two-family dwelling shall be supplied at all times between the hours of six a.m. and midnight with hot water at a constant minimum temperature of one hundred twenty degrees Fahrenheit from a central source of supply constructed in accordance with the provisions of the building code and the regulations of the department, provided however that baths and showers equipped with balanced-pressure mixing valves, thermostatic mixing valves or combination pressure balancing/thermostatic valves may produce a discharge temperature less than one hundred twenty degrees Fahrenheit but in no event less than one hundred ten degrees Fahrenheit. Gas or electric water heaters may, if approved by the department, be utilized in lieu of a central source of supply of hot water if such heaters:

(1) are lawfully in use on July fourteenth, nineteen hundred sixty-seven; or

(2) are approved by the appropriate city agencies having jurisdiction and are installed in a structure or building erected, converted, substantially rehabilitated, or completely vacated after July fourteenth, nineteen hundred sixty-seven.