I had a floating heater that failed me last year. It just coulnd't keep up with the severe cold temps and I lost ALL my big koi.
While ona pond tour this summer I asked everyone with big ponds how they handled the winter.Every one of them told me they take thier pupmp out, shut down the falls and run a LARGE aerator. They said a heater will eventually fail (I ran mine 3 years, without trouble, but it did eventually fail me) but an aerator will not.
I got a pondmaster 60, I have about 3000 gallons. I have about 6 air stones around different spots in the pond. I have 3-4 openeings all the time now, even with 18 inches of snow and absolutely freezing temps, I am a believer. Another plus, its cheaper to runt han the heater too!