I'm glad that your Icelandics do well with that management plan, but I wouldn't recommend it, or try it myself with my birds of other breed types.
Mary
That's why I use the old style metal waterers, with heater metal bases. They have worked fine here in -15F weather. I have two set up in the coop, so if one fails, there's another.
Heated dog dishes work fine too, as long as you don't have little chicks, or roosters with large wattles.
Mary