I have to keep refilling the two waterers for our 8 ducks every couple hours because their little pond froze solid and the waterers keep getting slushy.
Each time I refil them, they take turns swimming in them. The wind chill here is -8 and they have ice crystals on their feathers from swimming. I was about to make a thread asking if I should find something smaller for water to keep them from swimming, but I the posts here answered that question...silly ducks!
Mine have an 8x4 A frame house with two bales of straw and a bag of pine shavings on the floor....no heat lamp. They seemed to survive the frigid night ok.