| Constant | Description |
| STEAMINJECTION | Water vapor is added into the airstream through direct steam injection. |
| ADIABATICAIRWASHER | Water vapor is added into the airstream through adiabatic evaporation using an air washing element. |
| ADIABATICPAN | Water vapor is added into the airstream through adiabatic evaporation using a pan. |
| ADIABATICWETTEDELEMENT | Water vapor is added into the airstream through adiabatic evaporation using a wetted element. |
| ADIABATICATOMIZING | Water vapor is added into the airstream through adiabatic evaporation using an atomizing element. |
| ADIABATICULTRASONIC | Water vapor is added into the airstream through adiabatic evaporation using an ultrasonic element. |
| ADIABATICRIGIDMEDIA | Water vapor is added into the airstream through adiabatic evaporation using a rigid media. |
| ADIABATICCOMPRESSEDAIRNOZZLE | Water vapor is added into the airstream through adiabatic evaporation using a compressed air nozzle. |
| ASSISTEDELECTRIC | Water vapor is added into the airstream through water heated evaporation using an electric heater. |
| ASSISTEDNATURALGAS | Water vapor is added into the airstream through water heated evaporation using a natural gas heater. |
| ASSISTEDPROPANE | Water vapor is added into the airstream through water heated evaporation using a propane heater. |
| ASSISTEDBUTANE | Water vapor is added into the airstream through water heated evaporation using a butane heater. |
| ASSISTEDSTEAM | Water vapor is added into the airstream through water heated evaporation using a steam heater. |
| USERDEFINED | User-defined humidifier type. |
| NOTDEFINED | Undefined humidifier type. |