Details test and examination criteria for gas unit heaters and gas-fired duct furnaces for use with nat, mfd. and mixed gases, LP gases, and LP gas-air mixtures. A unit heater may either be suspended or floor-mounted and may be of the low- or high-static pressure type. Duct furnaces are normally installed in distribution ducts of air conditioning systems to supply warm air for heating and depended for air circulation on a blower not furnished as a part of the furnace.