HQRP® UHS24 Universal Humidifier Solenoid Valve 24V. Aprilaire 4040, GeneralAire 990-53, Honeywell 32001639-002, Carrier 4357, HE220 HE260 HE360, Fits Most Whole-House Units. Aprilaire: 400, 500, 550, 560, 600, 700.
eBay