| Code | Description |
| MG | Gas engine (internal combustion) |
| FA | Direct fired heater |
| FE | Cabin furnace |
| FF | Special furnace |
| FG | Water-tube boiler, fire-tube boiler, drum boiler |
| FJ | Incinerator (including thermo disposal equipment and evaporating candles) |
| FL | Economizer |
| FX | Burner |
| FY | Indirect fired heater |
| GD | Water Boiler/Heater |
| HD | Quench boiler/cooler |
| HE | Recovery boiler |
| HS | Water cooler |
| HT | Super heater |
| HW | Waste heat recovery unit |
| HM | Electric exchanger (not sanitary) |
| HN | Electric heating system applied to equipment |
| FR | Glycol regenerator |
| VA | Horizontal/Vertical pressure vessel (general) |
| VB | Expansion tank, Pressurizer, Compensation tank, Expansion vessel, Damper |