Steam generators are designed to add moisture to indoor air. They can use electricity, natural gas, propane, or even pressurized steam as an energy source. DriSteem offers a full range of systems for steam generation: GTS® (gas-to-steam) humidifiers that are the industry's best-selling gas-fired humidifier, electric steam humidifiers offering endless flexibility anywhere electricity is available, and STS® (steam-to-steam) humidifiers that create chemical-free humidification steam using boiler steam as the energy source.