The Humicontrol gas-powered steam humidifier fromCarel, LLC, (Lancaster, PA) has 20% to 100% modulation with combustion efficiency at 94%. It is designed to automatically detect excessive buildup of mineral scale on the heat exchanger, and has a water preheat circuit to allow the unit to respond to demand in seconds. The unit can process any kind of water, including demineralized, and is classified as a low NOx unit, and can use either natural gas or propane.