Now we're dealing with single-digit and sub-zero weather, and the water will freeze faster than I'm able to make myself available to swap them out, so I've gone ahead and purchased a heated drinker base:
http://www.fleetfarm.com/detail/harris-farms-heated-drinker-base/0000000249929
Two things I don't like: it smells, probably burning off oils that were put on it to keep it from rusting while warehoused, and 2, it's really hot. Water is near warm enough to bath in.
This weekend I'll see about solving the latter by placing some thin plywood in between the waterer and it.
Also, right now my chickens aren't going outside the coop. Its their first winter, and we've had high winds and snow. I think they'll venture out again when the winds calm and the sun comes out, but for now they won't do it. So the waterer is inside they're coop, and I haven't decided how much I trust that base yet. The bottom is made out of a heavy cardboard: not water-proof. So if water is spilled and it gets wet, I think I risk an electrical short and possible fire. However the thing isn't made (again, cardboard bottom) to be outside.
I may fix a sheet of plywood to the base, sealing it with silicone caulk or something, to make it safer.
One thing I do like about it, that so far trumps other concerns: my chickens have water. While I work from home, I still don't have time to keep them with liquid water at these temps.
