-7 is the lowest for the next week but I imagine we'll see -15 before winter is over
Thank you for all the input! This definitely eases my mind!! They are all healthy adults but they are silkies and one is a naked neck lol we're new to silkies.
For those temperatures, and considering that the chickens are Silkies and one has a naked neck:
Silkie feathers do blow around more easily than other feathers. I probably would make sure their sleeping area is draft-free (as in, no breezes strong enough to ruffle the Silkie feathers). This does not mean blocking all air from the coop. Ventilation it still very important. It just means checking how the air blows, and making sure it passes by the area where they will sleep. To check for drafts, some people peek at the chickens during the night to see if their feathers are blowing, other people hold a string or ribbon or plastic bag and watch how it moves.
Providing a heat source may be a good idea. I would try to put it in one corner of the coop, and I would try to make sure they are able to sleep near it or away from it (so two roosts or two sheltered corners, one warm and one unheated, to provide a choice of sleeping spots). You can watch where they choose to sleep, and after a while you will know if the heater is needed, appreciated, or unwanted. You might find that some chickens have different preferences than others.
Temperature conversions, for anyone else who (like me) is used to thinking in Fahrenheit instead of Celsius:
15 C is 59 F (what the chickens were used to)
0 C is 32 F (point where water freezes into ice)
-7 C is 19.4 F (expected low temperature in the next week)
-15 C is 5 F (expected low temperature before winter ends)
-17.8 C is 0 F (added so the list will have 0 in both temperature scales)