The Clean Comfort 12 GPD humidifier w/ manual Thermostat - HE12M provides whole-home humidification and use the warm air from the furnace or air handler to evaporate water that is trickled over an internal humidifier pad. The "M" model delivers humidity to meet the humidity target set manually by the homeowner or HVAC professional. HE12M bypass evaporative humidifiers have 12 gallon per day capacity.