This standard details test and examination criteria for forced-air type central furnaces and forced-air direct vent type central furnaces for use with natural, manufactured and mixed gases, liquefied petroleum gases and LP gas-air mixtures. Central furnaces are designed to supply heated air through ducts to spaces remote from or adjacent to the appliance location. Direct vent construction is such that all air for combustion
is obtained from outside the structure and flue gases are discharged outside the structure.
The harmonized standard also covers central furnaces equipped with automatic vent damper devices and for installation in manufactured homes, recreational vehicles (direct vent appliances), manufactured buildings, and outdoor installations.