34 HEATING AND AIR CONDITIONING APPARATUS-NAMELY, BOILERS, GRAVITY AND FORCED - AIR FURNACES, [ CONVERSION BURNERS, UNIT HEATERS, ] DEHUMIDIFIERS, [ WATER HEATERS, RADIANT HEATERS, ] COMBINED HEATING AND COOLING AIR CONDITIONERS, FLOOR FURNACES, ATTIC FURNACES, AND IGNITION, PILOT, AND ENTRAINMENT CONTROL DEVICES FOR GAS-FIRED BURNERS