i am also assuming your chickens...if they are layers...are 1-3 years old and not 10 years old. obviously, if you have chickens way past their optimal production period, drastic weather change might not help them...but your risk is low.
with that many birds huddled together you won’t need to heat the coop. keep the roost space tight...and you could have multiple open air “windows” that you close during the coldest times and leave open the rest of the year.
if they all roost together and there’s no direct wind draft across the roost...you’ll be fine. i live in oregon and knie people who have several of these chickens in central oregon. i would just not oversize your coop so that they’re own body heat also warms it up and use bedding during the winter.