I have used 2 Xtreme Heaters L in our 2007 Sea Ray 320 Sundancer for the past 12 years. I have never had an issue with freeze up and in fact for the most part they have maintained our bilge around 40-45 degrees in our coldest winters. I will admit I have looked to these heaters as backup as I always winterize. Then along came 2021 and the coldest record setting week in the history of Oklahoma. Temperatures maintained well below freezing for nine straight days with a rolling blackout (electrical cutoff) on the coldest morning of -15 degrees. Ok folks first this was the first year I did not winterize my engines, we have had mild winters up to this year and we had planned on using our boat on those nice winter days, but nine days of subzero temps got this boat owner a puckering. For three days the ice covered the dock so I could get down to our boat, then our boats frozen in lake, when we finally could get down the ramp the docks and boats didn’t move, frozen solid.