Chilly at that hour ! I used 6" PVC heavy couplings, and trouble lights to keep all my 5 gal. waters from freezing, even at 5 degrees. Epoxy coupling to 18" square of plywood, Use 2 " hole drill bit to cut hole for trouble light.Put 40 W. bulb in trouble light. Put waterer on top of PVC, and turn on the light. End of problem .For lower temps, you can use a 60 W. bulb.
The 40 w. bulbs keep the birds' water pleasantly tepid, and the birds don't have to expend energy heating up cold water in their crops. Having filled feeders the night before, and knowing that the birds do have fresh water, I have the luxury of not having to go out at 0 dark 30. I get a cup of hot coffee, and then go out, when the sun comes up. Win, win.