... , one is single speed, one is variable speed circulation.Product descriptionStainless steel casing, big air flowing, long life ... models are available.NameModelVoltageFrenquencyPowerRMPAir flowFLC circulation fan ZLFJ400220V 50HZ 145W1400r/min 2880m3/hFLC circulation fan ZLFJ500 222V/110V 50HZ ... 50HZ 45-100W 780-1320r/min2820 - 5200m3/hFLC Circulation fan variable speed ZLFJ500T 220V/110V 50HZ 45-100W ...