§ 139. Boiler rooms. In every dwelling the boiler or furnace of a central heating plant shall be enclosed in a fireproof room or space and all openings therefrom to other portions of the dwelling shall be equipped with fireproof doors and assemblies with the doors self-closing, except that in any dwelling three stories or less in height, such room or space may in the alternative be enclosed with walls or partitions constructed of fire-resistive materials and the ceiling fire retarded.