Section 27-419. Enclosure

Boilers  or furnaces hereafter installed in any
  building, other than replacement boilers and  furnaces  and  boilers  or
  furnaces  used  to  heat one- or two-family dwellings, shall be enclosed
  and  separated  from  the  rest  of  the  building   by   noncombustible
  construction  having  at least a one hour fire-resistance rating, except
  that:
    (a) All boilers carrying more than fifteen psi pressure and  having  a
  rating  in  excess  of  ten  horsepower,  shall  be located in a room or
  compartment separated from the rest of the  building  by  noncombustible
  construction having at least a two hour fire-resistance rating.
    (b)  Boilers  or  furnaces  located adjacent to, or within, automotive
  repair shops, public garages (group 1), or any occupancy  classified  in
  high hazard occupancy group A shall be located in separate buildings or,
  in  rooms  enclosed by noncombustible construction having at least a two
  hour fire-resistance rating. Entrance to such enclosed  rooms  shall  be
  from  the  outdoors,  or through an intervening vestibule constructed of
  materials having a two hour fire-resistance. rating. The floor  area  of
  such  vestibules  shall be at least fifty square feet, but not more than
  seventy-five square feet. Ventilation shall  be  provided  by  a  louver
  permanently  open  to  the  outdoor  air  having  a net free area of one
  hundred forty-four square inches,  located  near  the  floor.  Vestibule
  doors shall be one and one-half hour self-closing fire doors, with a six
  inch high sill provided at the door between the vestibule and the boiler
  room. Both doors shall swing in the direction of the boiler room.
    (c)  Boilers  having  a  rated gross capacity of less than sixty-seven
  thousand btu per hour for generating steam shall not be required  to  be
  enclosed, except as provided in subdivision (b) of this section.
    (d)  Electric  or  fuel-fired  space heaters need not be enclosed when
  they are approved for installation without enclosure and  are  installed
  in accordance with the conditions of approval.
    (e)  Boilers  and  furnaces  used  in  conjunction with commercial and
  industrial processes need not be enclosed, subject to  the  approval  of
  the commissioner.