Section 27-804. General requirements

All floor mounted combustion or heating
  equipment shall be mounted on noncombustible construction as provided in
  reference  standard  RS  14-17  or  on  combustible construction if such
  construction is protected as required in reference  standard  RS  14-17,
  provided the following conditions are met:
    (a)  All  clearances  shall  comply with the requirements specified in
  section 27-792 of article one of this subchapter.
    (b)  Heating  and  combustion  equipment  which  has  been  tested  in
  accordance with applicable standards listed in reference standard RS-14,
  shall be installed with the clearances determined by such tests.
    (c)  Equipment  which has been approved, as provided in section 27-135
  of article eight of subchapter one of this chapter, shall  be  installed
  in accordance with the conditions of such approval.
    (d)  When  mounted  above  combustible  construction, the equipment is
  arranged so that flame or gaseous products of combustion do not  impinge
  upon the base of the equipment.