I don't heat mine, and went with black rubber and this what I have found, down to the high twenties, the black would absorb enough heat to keep the water open during the day, little ice on top at night. But below 25 degrees, and it would freeze pretty hard and the nipples would not work.
I dumped the water at dark, and carried down warm water in the morning. Once it got into the teens, I cannot use the nipples. I go to the smaller black rubber bowls. They will freeze solid by late afternoon.
I don't have electricity at my coop, which keeps me from having electrical fires. But only limited warm water for my girls. They seem to do fine.
Mrs K