A central heating furnace shall be installed in accordance with the manufacturer's instructions and shall be installed on a floor of noncombustible construction with noncombustible flooring and surface finish and with no combustible material against the underside thereof, or on fire-resistive slabs or arches having no combustible material against the underside thereof.
Exceptions:
1. Appliances listed for installation on a combustible floor.
2. Installation on a floor protected in an approved manner.