N.Y.C. Admin. Code § 27-818: § 27-818 Enclosures.

Enclosures of floor furnaces shall be constructed entirely of noncombustible materials with a fire resistance rating of at least one hour and the enclosure shall be provided with adequate outdoor air in accordance with the requirements of article nine of this subchapter to ensure proper combustion. The enclosure shall be provided with adequate means of access for servicing the furnace.