It's currently 30 below this evening. I went out to my 5000 gallon pond and there's plenty of open water. Been super cold for a week and complete water about 7 by 6 foot. Perfect for not freezing solid and breaking my liner and for letting the decay gasses out. Love it
So far we haven't had any issues with freezing over even a part of the horse water tank. 150 gallons. I got this because my 1250 watt floating heater couldn't keep most of the surface ice free when nights dipped to 0 degrees, and I wanted to try a higher wattage. We will see if this one can handle -20 and wind blowing. That's why I bought it. The weather hasn't thrown us a real test yet.