Oh I wanted to say in the winter I use the rubber dishes that if the water gets frozen in you can just flip it over and stomp on it and the ice comes out and the bowl doesn't break. Really love those in the winter.
I am trying to find a picture of a heater that someone here in MN uses that is...
I have had -25 for 3 night in a row and I do not heat. Heat lamps can be very dangerous if they happen to fall.
Heating the coop is up to you. But I would not house the ducks and chickens together. The ducks make a mess with the water creating a bad scenario for moisture buildup in the coop...
I keep the ducks and chickens housed separately. They make such a mess with water and the chickens need it dry! Are your ducks young? Do they need heat? I live in Northern Minnesota and do not heat the coop or duck house. I go out and refresh water as needed if we are in an major cold spell...