| 1/00 | Feed-water heaters, e.g. preheaters |
| 1/02 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) |
| 1/04 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) the tubes having plain outer surfaces, e.g. in vertical arrangement |
| 1/06 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) the tubes having plain outer surfaces, e.g. in vertical arrangement in horizontal arrangement |
| 1/08 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) the tubes having fins, ribs, gills, corrugations, or the like on their outer surfaces, e.g. in vertical arrangement |
| 1/10 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) the tubes having fins, ribs, gills, corrugations, or the like on their outer surfaces, e.g. in vertical arrangement in horizontal arrangement (hollow fire-bars, grates, or the like used as water tubes F23H 3/02) |
| 1/12 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) Control devices, e.g. for regulating steam temperature |
| 1/14 | Feed-water heaters, e.g. preheaters with water tubes arranged in the boiler furnace, fire tubes, or flue ways (heat-exchange tubes in general F28F) Safety or venting devices (safety devices for boilers in general F22B 37/42) |
| 1/16 | Feed-water heaters, e.g. preheaters with water tubes arranged otherwise than in the boiler furnace, fire tubes, or flue ways |
| 1/18 | Feed-water heaters, e.g. preheaters with water tubes arranged otherwise than in the boiler furnace, fire tubes, or flue ways and heated indirectly |
| 1/20 | Feed-water heaters, e.g. preheaters with water tubes arranged otherwise than in the boiler furnace, fire tubes, or flue ways and directly connected to boilers |
| 1/22 | Feed-water heaters, e.g. preheaters with water tubes arranged otherwise than in the boiler furnace, fire tubes, or flue ways and provided for rotary movement |
| 1/24 | Feed-water heaters, e.g. preheaters with fire tubes or flue ways traversing feed-water vessels |
| 1/26 | Feed-water heaters, e.g. preheaters with means, other than tubes, to separate water and heating medium, e.g. bulk heaters without internal flues or tubes, jacketted smoke-boxes or flues |
| 1/28 | Feed-water heaters, e.g. preheaters for direct heat transfer, e.g. by mixing water and steam |
| 1/30 | Feed-water heaters, e.g. preheaters for direct heat transfer, e.g. by mixing water and steam with stages, steps, baffles, dishes, circular troughs, or other means to cause interrupted or cascading fall of water |
| 1/32 | Feed-water heaters, e.g. preheaters arranged to be heated by steam, e.g. bled from turbines |
| 1/34 | Feed-water heaters, e.g. preheaters arranged to be heated by steam, e.g. bled from turbines and returning condensate to boiler with main feed supply |
| 1/36 | Feed-water heaters, e.g. preheaters Water and air preheating systems |
| 1/38 | Feed-water heaters, e.g. preheaters Water and air preheating systems Constructional features of water and air preheating systems |