Furnace humidifier. Operating light lets you know when the unit is working. Easy wiring. Automatically cycles on/off with your furnace. Do-it-yourself installation. Includes: automatic humidistat, plug-in transformer, supply and drain tubing, bypass tube, collar and damper, low voltage harness and all necessary hardware. Fits on most forced air furnaces with 10-in. ducting. Easy left or right hand ducting. 12 US gal./24 h.