Cold cold cold!

[DuckMom2022]

I seem to keep saying this over and over but It's best to keep their swimming water or any large containers of water empty during severe temps so they don't sleep in the water overnight and it freeze around them which can cause them to get frostbite. If you feed inside of their coop just make sure what water you leave with them they can't climb into.

They have water in their coop. But when I lock them in at night, no food or water.

 

[DuckMom2022]

In Eastern Ontario, Canada, my winter temperature, Jan. to March are -20C/-4F. There is also an average 250cm/98inches of snow. The ducks, peacocks, chickens and guinea fowl all do fine. Each group has a coop with an attached run. They have a choice during the day where to spend their time and if the sun is shining they are out.
My ducks haven't had their swim pool for several months. I take out fresh water for them each morning in a container big enough to submerse their heads. No water in the coop at night.
IMO the important thing is that they are protected from winds and freezing rain. I tarp the side of runs where the prevailing winds are. Ducks are equipped to survive the cold with feather coverage (think down blankets and coats) and adapted circulation system.
From the description given by DuckMom2022, I would actually be more concerned that there might not be enough air circulation. I think excess humidity is a greater risk than the cold.

I actually have two vents that are about 3 inches by 12 inches on the top section of 2 sides of the house. They are covered in a good gauge wire to keep critters from getting in.

 

[DuckMom2022]

don’t forget ventilation overnight when they are locked in a small insulated building there has to be ventilation for the damp air to escape because they breathe out a lot of humidity . Windows up high one square foot per bird, covered in hardware cloth.

I have two windows about 3 inches tall x 12 long on the top of the 2 side walls of the house. Both covered in hardware cloth.